#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    int n;
    cin>>n;
    double distance,fuel;
    double totalDistance=0,totalFuel=0;
    for(int i=0;i<n;i++){
        cin>>distance>>fuel;
        if(distance<=0){
            cout<<"Invalide Distance";
            return 0;
            
        }
        if(fuel<=0){
            cout<<"Invalid Fuel";
            return 0;
        }
        totalDistance += distance;
        totalFuel+=fuel;
    }
    cout<<fixed<<setprecision(2)<<(totalDistance/toatlFuel);
    return 0;
}