by hansang(scy20250226修改):

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=1e4+10;
struct node{int x, f; LL c;} a[N]; 
bool operator<(node n1, node n2){return n1.c > n2.c;}
int main()
{
    int K, e, n; scanf("%d%d%d", &K, &e, &n);
    priority_queue<node> Q;
    for(int i=1; i<=n; i++)
    {
        scanf("%d%d%lld", &a[i].x, &a[i].f, &a[i].c);a[i].c += e - a[i].x;
        Q.push(a[i]);
    }
    LL ans=0; 
    while(K>0)
    {
        node no=Q.top();
        if(no.f <= K)
        {
            K -= no.f;
            ans += no.f * no.c;
            Q.pop();
        }
        else
        {
            ans += K * no.c;
            break;
        }
    }
    printf("%lld\n", ans);
    return 0;
}