#include<bits/stdc++.h>
using namespace std;
 
int main(){
	 int x,b[15];
	   cin>>x;
	 double a[15],sum=0; 
	 for(int i=1;i<=x;i++){
	 		cin>>a[i]>>b[i];
	 		sum+=a[i]*b[i]*1.0;
	 }
	   sum=sum*0.85;
	   cout<<fixed<<setprecision(1)<<sum;
}