#include<bits/stdc++.h>
using namespace std;
struct s
{
  float  m , w , z ;
} a[105] ;
float n , t , tt , sum ;
int main()
{
  cin >> n >> t ;
  for(int i = 1 ; i <= n ; i ++ )
  {
  	cin >> a[i].m >>a[i].w ;
  	a[i].z = a[i].w / a[i].m ; 
  }
  int i = 1 ;
  while ( tt < t )
  {
  	if( tt + a[i].m <= t )
  	{
  		sum += a[i].w ;
  		tt += a[i].m ;
  	}
  	else
  	{
  		sum += ( t - tt ) * a[i].z ;
  		tt = t + ( t - tt ) ;
  	}
  }
  printf ( "%.2f" , sum ) ;
  return 0; 
}