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

int main(){
    int n;
    cin >> n;
    
    if (n <1 || n > 50){
        return 0;
    }
    double totalDistance = 0.0;
    double totalFuel = 0.0;
    
    for (int i - 0; i< n; i++){
        double distance, fuel;
        cin >> distance >> fuel;
        
        if (distance <= 0){
            cout << "Invalid Distance";
            return 0;
        }
        if (fuel <= 0){
            cout << "Invali Fuel";
            return 0;
        }
        totalDistance += distance;
        totalFuel += fuel;
    }
    double efficieny = totalDistance / totalFuel;
    cout << fixed << setprecision(2) << efficiency;
    return 0;
}