HDU 1009 FatMouse' Trade

#include <stdio.h>
#include<iostream>
#include<algorithm>
using namespace std;
const int MAXN=1000;
struct Rooms
{
int j,f;
double rate;
}a[MAXN+1];
int cmp( Rooms p, Rooms q)
{
return p.rate > q.rate;
}
int main()
{
// freopen("input.txt","r",stdin);
// freopen("output.txt","w",stdout);
int M,N;
while(scanf("%d%d",&M, &N),M!=-1 || N != -1)
{
for(int i=0; i < N; i++)
{
scanf("%d%d",&a[i].j,&a[i].f);
a[i].rate = (a[i].j * 1.0)/ a[i].f;
}
sort(a,a+N,cmp);
double sum ,tot;
sum = tot =0;
for(int i=0; i < N; i++)
{
sum += a[i].j;
tot += a[i].f;
if(tot == M)  break;
if(tot > M)
{
tot -= a[i].f;
sum -= a[i].j;
sum += (((M-tot)*1.0/a[i].f)*a[i].j);
break;
}

}
printf("%.3lf/n",sum);
}
return 0;
}