#include<iostream>
#include<algorithm>
using namespace std;
struct b{
	int zh;
	int $;
};
int cmp(b x,b y){
	return x.$*y.zh>y.$*x.zh;
}
int main(){
	int n,m,i=0;
	float ans=0;
	cin>>n>>m;
	b a[n+10];
	for(i=0;i<n;i++)
		cin>>a[i].zh>>a[i].$;
	sort(a,a+n,cmp);
	while(i--){
		if(m>=a[i]){
			ans+=a[i];
			m-=a[i];
		}
        else
        break;
	}
	if(i>0){
		ans+=1.00*c/a[i].zh*a[i].$;
	}
	printf("%.2lf",ans);
	return 0;
}