FatMouse' Trade tzc

#include<cstdio>
#include<vector>
#include<algorithm>
using namespace std;

struct info
{
    double j;
    double f;
};

bool cmp(info a,info b)
{
    if(a.j/a.f > b.j/b.f) return 1;
    else return 0;
}

int main()
{
    int m,n;
    double sum;
    info t;
    vector<info> s;
    while(scanf("%d %d",&m,&n),m+n!=-2)
    {
        sum=0;
        for(int i=0;i<n;i++)
        {
           scanf("%lf %lf",&t.j,&t.f);
           s.push_back(t);
        }
        sort(s.begin(),s.end(),cmp);
        for(int i=0;i<s.size();i++)
        {
            if(s[i].f<=m) {m-=s[i].f;sum+=s[i].j;}
            else {sum+=m*s[i].j/s[i].f;m=0;}
        }
        printf("%.3lf\n",sum);
        s.clear();
    }
    return 0;
}