【杭电】[1009]FatMouse' Trade

#include<stdio.h>
#include<algorithm>
using namespace std;
struct node {
int j,f;
double m;
} a[1200];
bool cmp(node A,node B) {
return A.m>B.m;
}
int main() {
int m,n;
while(scanf("%d %d",&m,&n),m!=-1||n!=-1) {
double sum=0;
for(int i=0; i<n; i++) {
scanf("%d %d",&a[i].j,&a[i].f);
if(a[i].f>0)
a[i].m=(double)a[i].j/a[i].f;
else {
a[i].m=0;
sum+=a[i].j;
}
}
sort(a,a+n,cmp);
for(int i=0; i<n; i++) {
sum+=min(m,a[i].f)*a[i].m;
m-=min(m,a[i].f);
}
printf("%.3lf\n",sum);
}
return 0;
}