#include<iostream>
#include<iomanip>
using namespace std;
itn 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(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;
}