P1208 求条awa

#include <bits/stdc++.h>
using namespace std;
struct node {
	int x, y;
}a[5005];
bool cmp(node a,node b){
	return a.x<b.x;
}
int main(){
	ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
	int n, m, cnt;
	cin >> n >> m;
	for (int i = 1; i <= m; i ++) {
		cin >> a[i].x >> a[i].y;
	}
	sort (a + 1, a + m + 1, cmp);
	for (int i = 1; i <= m; i ++) {
		if (a[i].y <= n) {
			cnt += a[i].x * a[i].y;
			n -= a[i].y;
		}
		else {
			cnt += a[i].x * (a[i].y - n);
			n = 0;
		}
		if (n == 0) {
			break;
		}
	}
	cout << cnt;
}