#include<iostream>
#include<cstdio>
using namespace std;
int m[1000],v[1000],z[1000],j[500];
int main()
{
	double N,T;
	cin>>N>>T;
	double num=0,ans=0;
	int small=-1;
	for(int i=1;i<=N;i++)
	{
		cin>>m[i]>>v[i];
		z[i]=v[i]/m[i];
		j[z[i]]=i; 
		if(z[i]>=small) small=z[i];
	}
	while(num!=T)
	{
	    for(int i=small;i>=1;i--) 
		{
		    num+=m[j[i]],ans+=v[j[i]];
		    if(num>T) ans-=i*(num-T),i=1,num=T; 
	    }
	} 
	printf("%.2lf",ans);
	return 0;
}