#include<bits/stdc++.h>
using namespace std;
int n;
double a,b,s;
int main(){
	cin>>n;
	while(n--){
		cin>>a>>b;
		s+=a*b;
	}
	s*=0.85;
	s*=10;
	s=int(s)*1.0/10;
	cout<<s;
	return 0;
}