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

class FuelEfficiency {
    private:
    static double totalDistance;
    static diuble totalFuel;
    
    public:
    statuc void calculate() {
        int n;
        cin >> n;
        
        totalDistance = 0;
        totaFuel = 0;
        
        for (int i = 0; i < n; i++) {
            double d, f;
            cin >> d >> f;
            
            if (d <=0) {
                cout << "Invalid Distance";
                return;
            }
            
            if (f <=0) {
                cout << "Invalid Fuel";
                return;
            }
            
            totalDistance += d;
            totalFuel += f;
        }
        
        double efficiency = totalDistance / totalFuel;
        cout << fixed << setprecision(2) << efficiency;
        
    }
};

double fuelEfficiency :: totalDistance = 0;
double fuelEfficiency :: totalFuel = 0;

int main() {
    FuelEfficiency :: calculate() ;
    return 0;
}