// editor5
#include<iostream>
#include<iomanip>
using namespace std;

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