#include<iostream>

using namespace std;
int main(){
int a,b,c;
cin>>a>>b;
int d[a];
int e[a];
int n;
int cnt=0;
for(int i=0;i<a;i++)
{int m,n;
cin>>m>>n;
d[i]=m;
e[i]=n/m;}

for(;;){int max=0;
for(int i=0;i<a;i++)
{
if(e[i]>max){max=e[i]; n=i;}}


if(b-d[n]<=0){d[n]=b;cnt+=d[n]*e[n];break;}
else{cnt+=d[n]*e[n];b-=d[n];}
e[n]=0;}
printf("%.2f",cnt*1.0);}