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

int main(){
    int n;
    cin >> n;
    double distance , fuel;
    double totalDistance = 0.0, totalFuel = 0.0;
    
    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;
}
         if (totalFuel == 0){
            cout << "Invalid Fuel";
            return 0;
        }
        float efficiency = totalDistance / totalFuel;
        cout << fixed << setprecision(2) << efficiency;

        return 0;

}