#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 << "Invalid Fuel";
            return 0;
        }
        
        totalDistance += distance;
        totalFuel += fuel;
    }
    
    double efficiency = totalDistance /
totalFuel;

    cout << fixed << setprecision(2) <<
efficienct;
 
        retrun 0;
    
}