#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)<<efficiency;
    
       return o;
}