## Editorial for Xử lý số nguyên lớn

Remember to use this editorial only when stuck, and not to copy-paste code from it. Please be respectful to the problem author and editorialist.
Submitting an official solution before solving the problem yourself is a bannable offence.

Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

#### Code mẫu của flashmt

const base=100000000;
digit=8;
maxk=130000;
type bignum=array[0..maxk] of int64;
var a,b,c,d,re:bignum;
e:array[1..1000] of char;
bg:boolean;

procedure rf(var a:bignum);
var s:string; i,m,j:longint; c:char; code:integer; t:int64;
begin
fillchar(a,sizeof(a),0);
while not eoln do
begin
inc(a[0]);
end;
m:=a[0] mod digit;
if m=0 then m:=digit;
a[0]:=(a[0]+digit-1) div digit;
s:='';
for i:=1 to m do s:=s+e[i];
val(s,t,code);
a[a[0]]:=t;
for i:=0 to a[0]-2 do
begin
s:='';
for j:=1 to digit do s:=s+e[m+j+i*digit];
val(s,t,code);
a[a[0]-i-1]:=t;
end;
end;

function big:boolean;
var i:longint;
begin
big:=a[0]>b[0];
if a[0]=b[0] then
begin
big:=true;
for i:=a[0] downto 1 do
if a[i]>b[i] then break
else
begin
if a[i]<b[i] then
begin
big:=false;
break;
end;
end;
end;
end;

procedure wr(var k:bignum);
var s:string; t,j,i:longint;
begin
for i:=k[0] downto 1 do
begin
if i<k[0] then
begin
str(k[i],s);
t:=length(s);
for j:=t+1 to digit do write(0);
end;
write(k[i]);
end;
writeln;
end;

procedure plus;
var i,max:longint; mem:int64;
begin
fillchar(c,sizeof(c),0);
mem:=0;
if a[0]>b[0] then max:=a[0] else max:=b[0];
for i:=1 to max do
begin
c[i]:=(a[i]+b[i]+mem) mod base;
mem:=(a[i]+b[i]+mem) div base;
end;
if mem>0 then
begin
inc(max);
c[max]:=mem;
end;
c[0]:=max;
wr(c);
end;

procedure minus;
var i,max:longint; mem:int64;
begin
fillchar(c,sizeof(c),0);
mem:=0;
if not bg then
begin
write('-');
d:=a; a:=b; b:=d;
end;
max:=a[0];
for i:=1 to a[0] do
begin
if a[i]<b[i]+mem then
begin
c[i]:=a[i]+base-b[i]-mem;
mem:=1;
end
else
begin
c[i]:=a[i]-b[i]-mem;
mem:=0;
end;
end;
while (c[max]=0) and (max>1) do dec(max);
c[0]:=max;
wr(c);
end;

procedure multi;
var i,j,max,maxr:longint; mem,t:int64;
begin
fillchar(re,sizeof(re),0);
maxr:=a[0];
for i:=1 to b[0] do
begin
mem:=0;
fillchar(c,sizeof(c),0);
c[0]:=a[0];
for j:=1 to a[0] do
begin
c[j]:=(a[j]*b[i]+mem) mod base;
mem:=(a[j]*b[i]+mem) div base;
end;
if mem>0 then
begin
inc(c[0]);
c[c[0]]:=mem;
end;
mem:=0;
for j:=1 to c[0] do
begin
t:=c[j]+re[j+i-1]+mem;
re[j+i-1]:=t mod base;
mem:=t div base;
end;
j:=c[0]+i-1;
if j>maxr then maxr:=j;
while mem>0 do
begin
inc(j);
if j>maxr then maxr:=j;
t:=mem+re[j];
re[j]:=t mod base;
mem:=t div base;
end;
end;
re[0]:=maxr;
wr(re);
end;

begin
rf(a);
rf(b);
bg:=big;
plus;
minus;
multi;
end.


#### Code mẫu của happyboy99x

a=int(input())
b=int(input())
print(a+b)
print(a-b)
print(a*b)


#include <bits/stdc++.h>

using namespace std;

// * BIG INTEGER

typedef vector<int> bigInt;
const int BASE = 1000;
const int LENGTH = 3;

// * Refine function
bigInt& fix(bigInt &a) {
a.push_back(0);
for (int i = 0; i + 1 < a.size(); ++i) {
a[i + 1] += a[i] / BASE; a[i] %= BASE;
if (a[i] < 0) a[i] += BASE, --a[i + 1];
}
while (a.size() > 1 && a.back() == 0) a.pop_back();
return a;
}

// * Constructors
bigInt big(int x) {
bigInt result;
while (x > 0) {
result.push_back(x % BASE);
x /= BASE;
}
return result;
}

bigInt big(string s) {
bigInt result(s.size() / LENGTH + 1);
for (int i = 0; i < s.size(); ++i) {
int pos = (s.size() - i - 1) / LENGTH;
result[pos] = result[pos] * 10 + s[i] - '0';
}
return fix(result), result;
}

// * Compare operators

int compare(bigInt &a, bigInt &b) {
if (a.size() != b.size()) return (int)a.size() - (int)b.size();
for (int i = 0; i < a.size(); ++i)
if (a[i] != b[i]) return a[i] - b[i];
return 0;
}

#define DEFINE_OPERATOR(x) bool operator x (bigInt &a, bigInt &b) { return compare(a, b) x 0; }
DEFINE_OPERATOR(==)
DEFINE_OPERATOR(!=)
DEFINE_OPERATOR(>)
DEFINE_OPERATOR(<)
DEFINE_OPERATOR(>=)
DEFINE_OPERATOR(<=)
#undef DEFINE_OPERATOR

// * Arithmetic operators

void operator += (bigInt &a, bigInt b) {
a.resize(max(a.size(), b.size()));
for (int i = 0; i < b.size(); ++i)
a[i] += b[i];
fix(a);
}

void operator -= (bigInt &a, bigInt b) {
for (int i = 0; i < b.size(); ++i)
a[i] -= b[i];
fix(a);
}

void operator *= (bigInt &a, int b) {
for (int i = 0; i < a.size(); ++i)
a[i] *= b;
fix(a);
}

void divide(bigInt a, int b, bigInt &q, int &r) {
for (int i = int(a.size()) - 1; i >= 0; --i) {
r = r * BASE + a[i];
q.push_back(r / b); r %= b;
}
reverse(q.begin(), q.end());
fix(q);
}

bigInt operator + (bigInt a, bigInt b) { a += b; return a; }
bigInt operator - (bigInt a, bigInt b) { a -= b; return a; }
bigInt operator * (bigInt a, int b) { a *= b; return a; }

bigInt operator / (bigInt a, int b) {
bigInt q; int r = 0;
divide(a, b, q, r);
return q;
}
int operator % (bigInt a, int b) {
bigInt q; int r = 0;
divide(a, b, q, r);
return r;
}

bigInt operator * (bigInt a, bigInt b) {
bigInt result (a.size() + b.size());
for (int i = 0; i < a.size(); ++i)
for (int j = 0; j < b.size(); ++j)
result[i + j] += a[i] * b[j];
return fix(result);
}

// * I/O routines

istream& operator >> (istream& cin, bigInt &a) {
string s; cin >> s;
a = big(s);
return cin;
}

ostream& operator << (ostream& cout, const bigInt &a) {
cout << a.back();
for (int i = (int)a.size() - 2; i >= 0; --i)
cout << setw(LENGTH) << setfill('0') << a[i];
return cout;
}

int main() {
bigInt a, b;
cin >> a >> b;
cout << a + b << endl;
if (a < b)
cout << '-' << b - a << endl;
else
cout << a - b << endl;
cout << a * b << endl;
return 0;
}


#### Code mẫu của RR

#include <vector>
#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <string>
#include <ctime>
using namespace std;

// base and base_digits must be consistent
const int base = 1000000000;
const int base_digits = 9;

struct bigint {
vector<int> a;
int sign;

bigint() :
sign(1) {
}

bigint(long long v) {
*this = v;
}

bigint(const string &s) {
}

void operator=(const bigint &v) {
sign = v.sign;
a = v.a;
}

void operator=(long long v) {
sign = 1;
if (v < 0)
sign = -1, v = -v;
for (; v > 0; v = v / base)
a.push_back(v % base);
}

bigint operator+(const bigint &v) const {
if (sign == v.sign) {
bigint res = v;

for (int i = 0, carry = 0; i < (int) max(a.size(), v.a.size()) || carry; ++i) {
if (i == (int) res.a.size())
res.a.push_back(0);
res.a[i] += carry + (i < (int) a.size() ? a[i] : 0);
carry = res.a[i] >= base;
if (carry)
res.a[i] -= base;
}
return res;
}
return *this - (-v);
}

bigint operator-(const bigint &v) const {
if (sign == v.sign) {
if (abs() >= v.abs()) {
bigint res = *this;
for (int i = 0, carry = 0; i < (int) v.a.size() || carry; ++i) {
res.a[i] -= carry + (i < (int) v.a.size() ? v.a[i] : 0);
carry = res.a[i] < 0;
if (carry)
res.a[i] += base;
}
res.trim();
return res;
}
return -(v - *this);
}
return *this + (-v);
}

void operator*=(int v) {
if (v < 0)
sign = -sign, v = -v;
for (int i = 0, carry = 0; i < (int) a.size() || carry; ++i) {
if (i == (int) a.size())
a.push_back(0);
long long cur = a[i] * (long long) v + carry;
carry = (int) (cur / base);
a[i] = (int) (cur % base);
//asm("divl %%ecx" : "=a"(carry), "=d"(a[i]) : "A"(cur), "c"(base));
}
trim();
}

bigint operator*(int v) const {
bigint res = *this;
res *= v;
return res;
}

friend pair<bigint, bigint> divmod(const bigint &a1, const bigint &b1) {
int norm = base / (b1.a.back() + 1);
bigint a = a1.abs() * norm;
bigint b = b1.abs() * norm;
bigint q, r;
q.a.resize(a.a.size());

for (int i = a.a.size() - 1; i >= 0; i--) {
r *= base;
r += a.a[i];
int s1 = r.a.size() <= b.a.size() ? 0 : r.a[b.a.size()];
int s2 = r.a.size() <= b.a.size() - 1 ? 0 : r.a[b.a.size() - 1];
int d = ((long long) base * s1 + s2) / b.a.back();
r -= b * d;
while (r < 0)
r += b, --d;
q.a[i] = d;
}

q.sign = a1.sign * b1.sign;
r.sign = a1.sign;
q.trim();
r.trim();
return make_pair(q, r / norm);
}

bigint operator/(const bigint &v) const {
return divmod(*this, v).first;
}

bigint operator%(const bigint &v) const {
return divmod(*this, v).second;
}

void operator/=(int v) {
if (v < 0)
sign = -sign, v = -v;
for (int i = (int) a.size() - 1, rem = 0; i >= 0; --i) {
long long cur = a[i] + rem * (long long) base;
a[i] = (int) (cur / v);
rem = (int) (cur % v);
}
trim();
}

bigint operator/(int v) const {
bigint res = *this;
res /= v;
return res;
}

int operator%(int v) const {
if (v < 0)
v = -v;
int m = 0;
for (int i = a.size() - 1; i >= 0; --i)
m = (a[i] + m * (long long) base) % v;
return m * sign;
}

void operator+=(const bigint &v) {
*this = *this + v;
}
void operator-=(const bigint &v) {
*this = *this - v;
}
void operator*=(const bigint &v) {
*this = *this * v;
}
void operator/=(const bigint &v) {
*this = *this / v;
}

bool operator<(const bigint &v) const {
if (sign != v.sign)
return sign < v.sign;
if (a.size() != v.a.size())
return a.size() * sign < v.a.size() * v.sign;
for (int i = a.size() - 1; i >= 0; i--)
if (a[i] != v.a[i])
return a[i] * sign < v.a[i] * sign;
return false;
}

bool operator>(const bigint &v) const {
return v < *this;
}
bool operator<=(const bigint &v) const {
return !(v < *this);
}
bool operator>=(const bigint &v) const {
return !(*this < v);
}
bool operator==(const bigint &v) const {
return !(*this < v) && !(v < *this);
}
bool operator!=(const bigint &v) const {
return *this < v || v < *this;
}

void trim() {
while (!a.empty() && !a.back())
a.pop_back();
if (a.empty())
sign = 1;
}

bool isZero() const {
return a.empty() || (a.size() == 1 && !a[0]);
}

bigint operator-() const {
bigint res = *this;
res.sign = -sign;
return res;
}

bigint abs() const {
bigint res = *this;
res.sign *= res.sign;
return res;
}

long long longValue() const {
long long res = 0;
for (int i = a.size() - 1; i >= 0; i--)
res = res * base + a[i];
return res * sign;
}

friend bigint gcd(const bigint &a, const bigint &b) {
return b.isZero() ? a : gcd(b, a % b);
}
friend bigint lcm(const bigint &a, const bigint &b) {
return a / gcd(a, b) * b;
}

sign = 1;
a.clear();
int pos = 0;
while (pos < (int) s.size() && (s[pos] == '-' || s[pos] == '+')) {
if (s[pos] == '-')
sign = -sign;
++pos;
}
for (int i = s.size() - 1; i >= pos; i -= base_digits) {
int x = 0;
for (int j = max(pos, i - base_digits + 1); j <= i; j++)
x = x * 10 + s[j] - '0';
a.push_back(x);
}
trim();
}

friend istream& operator>>(istream &stream, bigint &v) {
string s;
stream >> s;
return stream;
}

friend ostream& operator<<(ostream &stream, const bigint &v) {
if (v.sign == -1)
stream << '-';
stream << (v.a.empty() ? 0 : v.a.back());
for (int i = (int) v.a.size() - 2; i >= 0; --i)
stream << setw(base_digits) << setfill('0') << v.a[i];
return stream;
}

static vector<int> convert_base(const vector<int> &a, int old_digits, int new_digits) {
vector<long long> p(max(old_digits, new_digits) + 1);
p[0] = 1;
for (int i = 1; i < (int) p.size(); i++)
p[i] = p[i - 1] * 10;
vector<int> res;
long long cur = 0;
int cur_digits = 0;
for (int i = 0; i < (int) a.size(); i++) {
cur += a[i] * p[cur_digits];
cur_digits += old_digits;
while (cur_digits >= new_digits) {
res.push_back(int(cur % p[new_digits]));
cur /= p[new_digits];
cur_digits -= new_digits;
}
}
res.push_back((int) cur);
while (!res.empty() && !res.back())
res.pop_back();
return res;
}

typedef vector<long long> vll;

static vll karatsubaMultiply(const vll &a, const vll &b) {
int n = a.size();
vll res(n + n);
if (n <= 32) {
for (int i = 0; i < n; i++)
for (int j = 0; j < n; j++)
res[i + j] += a[i] * b[j];
return res;
}

int k = n >> 1;
vll a1(a.begin(), a.begin() + k);
vll a2(a.begin() + k, a.end());
vll b1(b.begin(), b.begin() + k);
vll b2(b.begin() + k, b.end());

vll a1b1 = karatsubaMultiply(a1, b1);
vll a2b2 = karatsubaMultiply(a2, b2);

for (int i = 0; i < k; i++)
a2[i] += a1[i];
for (int i = 0; i < k; i++)
b2[i] += b1[i];

vll r = karatsubaMultiply(a2, b2);
for (int i = 0; i < (int) a1b1.size(); i++)
r[i] -= a1b1[i];
for (int i = 0; i < (int) a2b2.size(); i++)
r[i] -= a2b2[i];

for (int i = 0; i < (int) r.size(); i++)
res[i + k] += r[i];
for (int i = 0; i < (int) a1b1.size(); i++)
res[i] += a1b1[i];
for (int i = 0; i < (int) a2b2.size(); i++)
res[i + n] += a2b2[i];
return res;
}

bigint operator*(const bigint &v) const {
vector<int> a6 = convert_base(this->a, base_digits, 6);
vector<int> b6 = convert_base(v.a, base_digits, 6);
vll a(a6.begin(), a6.end());
vll b(b6.begin(), b6.end());
while (a.size() < b.size())
a.push_back(0);
while (b.size() < a.size())
b.push_back(0);
while (a.size() & (a.size() - 1))
a.push_back(0), b.push_back(0);
vll c = karatsubaMultiply(a, b);
bigint res;
res.sign = sign * v.sign;
for (int i = 0, carry = 0; i < (int) c.size(); i++) {
long long cur = c[i] + carry;
res.a.push_back((int) (cur % 1000000));
carry = (int) (cur / 1000000);
}
res.a = convert_base(res.a, 6, base_digits);
res.trim();
return res;
}
};

int main() {
ios :: sync_with_stdio(false);
string A, B; cin >> A >> B;
bigint a(A);
bigint b(B);

cout << a + b << endl;
cout << a - b << endl;
cout << a * b << endl;
}


#### Code mẫu của hieult

#include <cstdlib>
#include <iostream>
using namespace std;
int a[3000],b[3000],c[3000],_a[3000],_b[3000],_c[3000],ti[3000],hi[3000],to[3000];
int a1,b1,c1,i,_a1,_b1,_c1;
int tong()
{
long tong,nho=0;
int i,j;
//int a[1000], b[1000], c[1000],a1, b1, c1;
a1=_a1;
b1=_b1;
for (i=1; i<=a1; i++) a[i]=_a[i];
for (i=1; i<=b1; i++) b[i]=_b[i];
for (i=1; i<=a1; i++) c[i]=a[i];
for (i=1; i<=a1; i++) a[i]=c[a1-i+1];
for (i=1; i<=b1; i++) c[i]=b[i];
for (i=1; i<=b1; i++) b[i]=c[b1-i+1];
if (a1>b1) c1=a1; else c1=b1;
for (i=a1+1; i<=c1; i++)a[i]=0;
for (i=b1+1; i<=c1; i++)b[i]=0;
for (i=1; i<=c1; i++)
{
tong=nho+a[i]+b[i];
c[i]=tong%10;
nho=tong/10;
}
if (nho>0) c1++, c[c1]=nho;
for (i=1; i<=c1; i++) a[i]=c[i];
for (i=1; i<=c1; i++) c[i]=a[c1-i+1];
for (i=1; i<=c1; i++) to[i]=c[i];
to[0]=c1;
}
int _hieu()
{
//int a[1000], b[1000], c[1000], a1, b1, c1;
long tong,nho=0,dau=1;
int i,j,tg;
a1=_a1;
b1=_b1;
for (i=1; i<=a1; i++) a[i]=_a[i];
for (i=1; i<=b1; i++) b[i]=_b[i];
for (i=1; i<=a1; i++) c[i]=a[i];
for (i=1; i<=a1; i++) a[i]=c[a1-i+1];
for (i=1; i<=b1; i++) c[i]=b[i];
for (i=1; i<=b1; i++) b[i]=c[b1-i+1];
if (a1>b1) c1=a1; else c1=b1;
for (i=a1+1; i<=c1; i++)a[i]=0;
for (i=b1+1; i<=c1; i++)b[i]=0;
for (i=c1; i>=1; i--)
if (a[i]!=b[i]){
if (a[i]<b[i])dau=-1; else dau=1;
break;
}
if (dau==-1){
for (i=1; i<=c1; i++){
tg=a[i];
a[i]=b[i];
b[i]=tg;
}
}
for (i=1; i<=c1; i++){
tong=10+nho+a[i]-b[i];
c[i]=tong%10;
if (tong/10>0) nho=0; else nho=-1;
}
while (c[c1]==0& c1>1)c1--;
for (i=1; i<=c1; i++) a[i]=c[i];
for (i=1; i<=c1; i++) c[i]=a[c1-i+1];
hi[c1+1]=dau;
hi[0]=c1;
for (i=1; i<=c1; i++) hi[i]=c[i];
}
int tich(){
//int a[1000], b[1000], c[1000], a1, b1, c1;
long tong=0,nho=0;
int i,j;
a1=0;b1=0;c1=0;
a1=_a1;
b1=_b1;
tong=0; nho=0;
for (i=1; i<=a1; i++) a[i]=_a[i];
for (i=1; i<=b1; i++) b[i]=_b[i];
for (i=1; i<=a1; i++) c[i]=a[i];
for (i=1; i<=a1; i++) a[i]=c[a1-i+1];
for (i=1; i<=b1; i++) c[i]=b[i];
for (i=1; i<=b1; i++) b[i]=c[b1-i+1];
c1=a1+b1;
for (i=1; i<=c1; i++) c[i]=0;
for (i=1; i<=c1; i++){
tong=nho;
for (j=1; j<=i; j++)
tong = tong + a[j]*b[i+1-j];
c[i]=tong%10;
nho=tong/10;
}
if (nho>0) c[c1]=nho;
if (c[c1]==0) c1--;
for (i=1; i<=c1; i++) a[i]=c[i];
for (i=1; i<=c1; i++) c[i]=a[c1-i+1];
ti[0]=c1;
for (i=1; i<=c1; i++) ti[i]=c[i];
}
int nhap(){
string st1,st2;
char ch='a';
cin>>st1;
cin>>st2;
a1=st1.length();
b1=st2.length();
for (i=0; i<a1; i++) a[i+1]=short(st1[i])-48;
for (i=0; i<b1; i++) b[i+1]=short(st2[i])-48;
for (i=1; i<=a1; i++) _a[i]=a[i];
for (i=1; i<=b1; i++) _b[i]=b[i];
_a1=a1;
_b1=b1;
}
int thu(){
tich();
tong();
_hieu();
for(i=1; i<=to[0]; i++) cout<<to[i]; cout<<endl;
if (hi[hi[0]+1]==-1) cout<<"-";
for(i=1; i<=hi[0]; i++) cout<<hi[i]; cout<<endl;
for(i=1; i<=ti[0]; i++) cout<<ti[i];
}
int main(int argc, char *argv[])
{
nhap();
thu();
//system("PAUSE");
return(0);
}


#### Code mẫu của ll931110

Program BIGNUM;
Const
input  = '';
output = '';
Type
arr = array[1..2000] of longint;
Var
a,b,c: arr;
k,m,n: integer;
fa: text;
ch: char;
i: integer;

Procedure init;
Var
f: text;
i: integer;
Begin
m:= 0;
n:= 0;

Assign(f, input);
Reset(f);
While not eoln(f) do
Begin
inc(m);
a[m]:= ord(ch) - 48;
End;
For i:= 1 to m do a[2000 - m + i]:= a[i];
m:= 2001 - m;

While not eoln(f) do
Begin
inc(n);
b[n]:= ord(ch) - 48;
End;
For i:= 1 to n do b[2000 - n + i]:= b[i];
n:= 2001 - n;
Close(f);

If m > n then k:= n else k:= m;
End;

Procedure printresult(p: integer);
Var
i: integer;
Begin
For i:= p to 2000 do write(fa, c[i]);
Writeln(fa);
End;

Var
i: integer;
Begin
Fillchar(c, sizeof(c), 0);

For i:= 2000 downto k do
Begin
c[i]:= c[i] + (a[i] + b[i]);
If c[i] > 9 then
Begin
inc(c[i - 1]);
c[i]:= c[i] - 10;
End;
End;

If c[k - 1] <> 0 then printresult(k - 1)
else printresult(k);
End;

Procedure subtract(x,y: arr);
Var
s,i: integer;
Begin
Fillchar(c, sizeof(c), 0);

For i:= 2000 downto k do
Begin
c[i]:= c[i] + (x[i] - y[i]);
If c[i] < 0 then
Begin
dec(c[i - 1]);
c[i]:= c[i] + 10;
End;
End;

s:= k;
While c[s] = 0 do inc(s);
printresult(s);
End;

Procedure minus;
Var
d: integer;
Begin
d:= k;
While (d <= 2000) and (a[d] = b[d]) do inc(d);

If d > 2000 then writeln(fa, 0) else
If a[d] > b[d] then subtract(a,b)
else begin
write(fa, '-');
subtract(b,a);
end;
End;

Procedure multiply;
Var
i,j,t: integer;
Begin
Fillchar(c, sizeof(c), 0);

For i:= 2000 downto m do
For j:= 2000 downto n do
Begin
t:= i + j - 2000;
c[t]:= c[t] + a[i] * b[j];
If c[t] > 9 then
Begin
c[t - 1]:= c[t - 1] + c[t] div 10;
c[t]:= c[t] mod 10;
End;
End;

t:= 1;
While c[t] = 0 do inc(t);
printresult(t);
End;

Begin
init;
Assign(fa, output);
Rewrite(fa);
minus;
multiply;
Close(fa);
End.


#### Code mẫu của skyvn97

#include<stdio.h>
#include<string.h>
#include<algorithm>
#define MAX   2611
using namespace std;
struct bignum
{
int nd;
int sb;
int d[MAX];
bignum()
{
nd=0;
}
bignum(int x)
{
if (x==0)
{
nd=1;
sb=1;
d[1]=0;
}
if (x>0)
{
nd=0;
sb=1;
while (x>0)
{
nd++;
d[nd]=x%10;
x=x/10;
}
}
if (x<0)
{
nd=0;
sb=-1;
x=-x;
while (x>0)
{
nd++;
d[nd]=x%10;
x=x/10;
}
}
}
bignum(const bignum &x)
{
nd=x.nd;
sb=x.sb;
int i;
for (i=1;i<=nd;i=i+1) d[i]=x.d[i];
}
void input(void)
{
char s[MAX];
scanf("%s",s);
sb=1;
nd=0;
int i;
for (i=strlen(s)-1;i>=0;i=i-1)
{
nd++;
d[nd]=s[i]-48;
}
}
void print(void)
{
if (sb<0) printf("-");
int i;
for (i=nd;i>=1;i=i-1) printf("%d",d[i]);
}
bignum abs()
{
bignum r=bignum(*this);
r.sb=1;
return (r);
}
int cmp(const bignum&x)
{
if (sb>x.sb) return (1);
if (sb<x.sb) return (-1);
if (nd>x.nd) return (sb);
if (nd<x.nd) return (-sb);
int i;
for (i=nd;i>=1;i=i-1)
{
if (d[i]>x.d[i]) return (sb);
if (d[i]<x.d[i]) return (-sb);
}
return (0);
}
bignum operator + (const bignum &x) // only compatible for non-negative integer
{
int n=max(nd,x.nd);
int i,s,c;
bignum res (*this);
res=bignum();
res.sb=1;;
s=0;c=0;
for (i=nd+1;i<=n;i=i+1) d[i]=0;
//for (i=x.nd+1;i<=n;i=i+1) x.d[i]=0;
for (i=1;i<=n;i=i+1)
{
s=d[i]+x.d[i]+c;
if (s>9) c=1;
else c=0;
res.nd++;
res.d[res.nd]=s%10;
}
if (c>0)
{
res.nd++;
res.d[res.nd]=1;
}
return (res);
}
bignum operator - (const bignum &x) // only compatible for non-negative integer
{
int tmp=cmp(x);
if (tmp>0)
{
bignum res;
res=bignum();
res.sb=1;
int i,s,c;
//for (i=x.nd+1;i<=nd;i=i+1) x.d[i]=0;
s=0;
c=0;
for (i=1;i<=nd;i=i+1)
{
s=d[i]-x.d[i]-c;
if (s<0)
{
s=s+10;
c=1;
}
else c=0;
res.nd++;
res.d[res.nd]=s%10;
}
while (res.d[res.nd]==0) res.nd--;
return (res);
}
if (tmp==0) return (bignum(0));
if (tmp<0)
{
bignum res;
res=bignum();
int i,s,c;
res.sb=-1;
s=0;c=0;
for (i=nd+1;i<=x.nd;i=i+1) d[i]=0;
for (i=1;i<=x.nd;i=i+1)
{
s=x.d[i]-d[i]-c;
if (s<0)
{
s=s+10;
c=1;
}
else c=0;
res.nd++;
res.d[res.nd]=s%10;
}
while (res.d[res.nd]==0) res.nd--;
return (res);
}
}
bignum operator * (const bignum &x) //compatible for all numbers
{
if ((nd==1) && (d[1]==0)) return (bignum(0));
if ((x.nd==1) && (x.d[1]==0)) return (bignum(0));
bignum res;
res=bignum();
res.sb=sb*x.sb;
int i,j,s,c;
for (i=1;i<=x.nd;i=i+1)
{
bignum tmp=bignum();
for (j=1;j<i;j=j+1)
{
tmp.nd++;
tmp.d[tmp.nd]=0;
}
s=0;c=0;
for (j=1;j<=nd;j=j+1)
{
s=d[j]*x.d[i]+c;
c=s/10;
tmp.nd++;
tmp.d[tmp.nd]=s%10;
}
while (c>0)
{
tmp.nd++;
tmp.d[tmp.nd]=c%10;
c=c/10;
}
res=res+tmp;
}
return (res);
}
};
bignum a,b,c;
int main(void)
{
a.input();
b.input();
c=a+b;
c.print();
printf("\n");
c=a-b;
c.print();
printf("\n");
c=a*b;
c.print();
printf("\n");
}


#### Code mẫu của khuc_tuan

import java.math.BigInteger;
import java.util.Scanner;

public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
BigInteger a = new BigInteger(sc.next());
BigInteger b = new BigInteger(sc.next());