#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    int n;
    cin>>n;
    double distance,fuel;
    double totalDistance = 0.0,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;
}