RT

#include<bits/stdc++.h>
using namespace std;

double a,ans;

int main()
{
	int n,b;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a>>b;
		ans+=a*0.85*b;
	}
	cout<<((int)(ans*10+0.01))/10.0;
	return 0;
}