//#include<bits/stdc++.h>
//#include<windows.h>
#include<iostream>
#include<iomanip>
using namespace std;
int main(){
   cout<<fixed<<setprecision(1);
   double zq=0,q;
   int n,s;
   cin>>n;
   for(int i=0;i<n;i++){
   	cin>>q>>s;
   	zq+=q*s;
   }cout<<zq*0.85;
   return 0;
}