#include<bits/stdc++.h>
using namespace std;
struct coin{
	int m;
	int v;
} ;coin a[9999];
bool cmp(coin c,coin b){
	return  c.v*b.m>c.m*b.v;
}
int main(){
	int n,bag,price=0;
	cin>>n>>bag;
	int i,j;
	for(i=1;i<=n;i++)
	cin>>a[i].m>>a[i].v;
	sort(a+1,a+n+1,cmp);
	for(i=1;i<=n;i++){
		if(a[i].m<bag){
			bag-=a[i].m;
			price+=a[i].v;
		}
		else{
			price+=a[i].v*1.0/(a[i].m*1.0)*bag;
			break;
		}
	}
	printf("%.2f\n",float(price));
	return 0;
} 

请各位大佬看一下，我已经改了半天了，球球您了，帮蒟蒻一下吧