Code mẫu

#include <bits/stdc++.h>

using namespace std;

#define fo(i, a, b) for(int i = a; i <= b; i++)
#define _fo(i, a, b) for(int i = a; i >= b; i--)
#define foa(i, a) for (auto &i : a)
#define sz(a) ((int) a. size())
#define all(a) begin(a), end(a)
#define fi first
#define se second
#define pb(x) push_back(x)
#define mk(x, y) make_pair(x, y)

typedef unsigned long long ull;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vl;
typedef pair<int, int> pii;
typedef vector<int> vi;

const int MAX = 1e5+5;
const int LOG = 20;
const ll MOD = 1e9+7;
const ll INF = 1e9+1;
const int SQRT = 44721;

ll add(ll a, ll b) { return (a+b) % MOD; }
ll sub(ll a, ll b) { return (a-b+MOD) % MOD; }
ll mul(ll a, ll b) { return (a % MOD)*(b % MOD) % MOD; }

ll inv(ll val) {
    ll curr = 1, temp = MOD-2;

    while(temp > 0) {
        if(temp & 1) curr = mul(curr, val);
        val = mul(val, val);
        temp >>= 1;
    }

    return curr;
}

ll comb(ll a, ll b) {
    if(b > a) return 0;
    b = min(b, a-b);
    ll temp = 1, fac = 1;
    fo(i, 1, b) temp = mul(temp, a-i+1);
    fo(i, 1, b) fac = mul(fac, i);
    return mul(temp, inv(fac));
}

ll candy(ll a, ll b) {
    return comb(a+b-1, b);
}

signed main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    ll n, k;
    cin >> n >> k;
    cout << candy((n/k)*2, n%k);
}

/*
1
2 2
0000
*/