#include <iostream>
#include <iomanip>
using namespace std;
int main(){
    int n;
    cin>>;
    double distance, fuel;
    double totalDistance = 0.0;
    double 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;
    }
    double efficiency = totalDistance / totalFuel;
    cout<<fixed<<setprecision(2)<<efficiency;
    return 0;
}