代码如下：

#include <bits/stdc++.h>
using namespace std;
struct node
{
	int m,v;
} a[105];
bool cmp(node p,node q)
{
	return p.v*q.m>q.v*p.m;
}
int n,t;
double ans;
int main()
{
	scanf("%d%d",&n,&t);
	for(int i=1; i<=n; ++i) scanf("%d%d",&a[i].m,&a[i].v);
	sort(a+1,a+n+1,cmp);
	for(int i=1; i<=n; ++i)
	{
		if(a[i].m<=t)
		{
			t-=a[i].m;
			ans+=a[i].v;
		}
		else
		{
			ans+=a[i].v*t*1.0/(a[i].m*1.0);
			break;
		}
	}
	printf("%.2llf",ans);
	return 0;
}