#include<iostream>
#include<iomanip>
using namespace std;

int main()
{
    int n;
    cin>>n;
    
    double Distance, Fuel;
    double totalDistance=0, totalFule=0;
    for(int i=0;i<n;i++)
    {
        cin>>Distance>>Fuel;
        if(Distance<=0)
        {
            cout<<"Invalid Distance";
            return 0;
        }
        if(Fuel<= 0)
        {
            cout<<"Invalid Fuel";
            return 0;
        }
        totalDistance+=Distance;
        totalFuel+=Fuel;
    }
    double efficiency= totalDistance / totalFuel;
    cout<<fixed<<setprcision(2)<<efficiency;
    return 0;
}