Code mẫu

//TrungNotChung
#include <bits/stdc++.h>
#define pii pair<int , int>
#define fi first
#define se second
#define BIT(x,i) (1&((x)>>(i)))
#define MASK(x)  (1LL<<(x))
#define CNT(x) __builtin_popcountll(x)
#define task "tnc"  

using namespace std;
const int N = (int)1e5+228;
const int INF = (int)1e9 + 7;

int n, m;
set<pii> s;
set<pii>::iterator itr;
pii a[N];

void solve()
{   
    cin >> n >> m;
    for(int i = 1; i <= n; ++i)
        cin >> a[i].fi >> a[i].se;
    sort(a + 1, a + n + 1, [&](const pii &x, const pii &y)
    {
        if(x.fi == y.fi)
            return x.se < y.se;
        return x.fi > y.fi;
    });

    s.insert(make_pair(1, m));
    long long res = 0;
    for(int i = 1; i <= n; ++i)
    {
        int p = m - a[i].se + 1;
        itr = s.upper_bound(make_pair(p, m+1));
        if(itr == s.begin())
            continue;
        --itr;
        int l = (*itr).fi;
        int r = (*itr).se;
        p = min(p, r);
        s.erase(make_pair(l, r));
        res += a[i].fi;
        if(l <= p - 1)
            s.insert(make_pair(l, p - 1));
        if(p + 1 <= r)
            s.insert(make_pair(p + 1, r));
    }
    cout << res;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    #ifndef ONLINE_JUDGE
    freopen(task".inp","r",stdin);
    freopen(task".out","w",stdout);
    #endif // ONLINE_JUDGE
    solve();
    //cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
    return 0;
}