#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
using namespace std;
float a[15];
int b[15];
int main()
{int n;
scanf("%d",&n);
for(int i=1;i<=n;i++)
  scanf("%f%d",&a[i],&b[i]);
float sum=0.0;
for(int i=1;i<=n;i++)
  sum=sum+a[i]*b[i];
sum=sum*0.85;
sum=(int)(sum*10);
sum=sum/10.0;
printf("%.1f",sum);
return 0;
}