#include<bits/stdc++.h>
using namespace std;  
int main(){
	double n,a[11],b[11],s[11],sum=0;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i]>>b[i];
		s[i]=a[i]*b[i];
		sum+=s[i];
	}cout<<fixed<<setprecision(1)<<0.85*sum;
	return 0;
}