【codevs1621】混合牛奶

problem

solution

codes

#include<iostream>
#include<algorithm>
using namespace std;
int N,M,ans,n;
struct nm{
    int Pi;
    int Ai;
}U[5050];
bool cmp( const nm a,const nm b){return a.Pi < b.Pi;}
int main(){
    cin >> N >> M;
    for(int i = 0;i<M;i++){cin >> U[i].Pi  >> U[i].Ai;}
    sort(U,U+M,cmp);
    for(int i = 0;i<M && N;i++){
        if(N > U[i].Ai)n = U[i].Ai;
        else n = N;
        ans += n * U[i].Pi;
        N -= n;
    }
    cout << ans << "\n";
    return 0;
}