#include<bits/stdc++.h>
using namespace std;
double n,s=0.0;
int main()
{
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		double x,y;
		cin>>x>>y;
		s+=x*y;
	}
	s*=0.85;
	printf("%0.1f",s);
}
/*10
54.86 1
84.49 8
31.40 6
63.87 4
75.92 5
84.81 7
16.27 6
81.28 7
54.85 1
99.58 8*/

那个注释的是样例3