永远一个点re

#include <iostream>
#include <algorithm>
using namespace std;
struct farmer
{
    int cost, number;
}a[5001];
int cmp(const farmer & a, const farmer & b)
{
    if(a.cost > b.cost) return 0;
    return 1;
}
int main()
{
    int m, ans = 1， n;
    long long tot = 0;
    cin >> n >> m;
    for(int i = 1; i <= m; ++i) cin >> a[i].cost >> a[i].number;
    sort(a + 1, a + m + 1, cmp);
    while(n > 0)
    {
        if(n > a[ans].number)
        {
            n = n - a[ans].number;
            tot = tot + a[ans].cost * a[ans].number;
        }
        else
        {
            tot = tot + a[ans].cost * n;
            break;
        }
        ans++;
    }
    cout << tot;
    return 0;
}