FatMouse' Trade

 太坑了这个题，还要考虑不花钱就可以兑换，哇塞，便宜都让老鼠给占了

Description

FatMouse prepared M pounds of cat food, ready to trade with the cats guarding the warehouse containing his favorite food, JavaBean. The warehouse has N rooms. The i-th room contains J[i] pounds of JavaBeans and requires F[i] pounds of cat food. FatMouse does not have to trade for all the JavaBeans in the room, instead, he may get J[i]* a% pounds of JavaBeans if he pays F[i]* a% pounds of cat food. Here a is a real number. Now he is assigning this homework to you: tell him the maximum amount of JavaBeans he can obtain.

Input

The input consists of multiple test cases. Each test case begins with a line containing two non-negative integers M and N. Then N lines follow, each contains two non-negative integers J[i] and F[i] respectively. The last test case is followed by two -1's. All integers are not greater than 1000.

Output

For each test case, print in a single line a real number accurate up to 3 decimal places, which is the maximum amount of JavaBeans that FatMouse can obtain.

Sample Input

5 3
7 2
4 3
5 2
20 3
25 18
24 15
15 10
-1 -1

Sample Output

13.333
31.500

代码：

#include <iostream>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
using namespace std;
struct node
{
    double a,b,v;
}s[100010];
bool cmp(struct node a,struct node b)
{
    return a.v>b.v;
}
int main()
{
    int n,i,j;
    double  m,k;
    while(scanf("%lf%d",&m,&n)!=EOF&&(m!=-1||n!=-1))
    {
        k=0;
        for(i=0;i<n;i++)
        {
            scanf("%lf%lf",&s[i].a,&s[i].b);
            if(s[i].b==0)
                s[i].v=s[i].a;
            else
                s[i].v=s[i].a/s[i].b;
        }
        sort(s,s+n,cmp);
        for(i=0;i<n;i++)
        {
            if(s[i].b<=m)
            {
                m-=s[i].b;
                k+=s[i].a;
            }
            else
            {
                if(m!=0)
                    k+=s[i].v*m;
                m=0;
            }
        }
        printf("%.3lf\n",k);
    }
    return 0;
}