#include<iostream>
#include<iomanip>
int main()
{
    int n;
    if(!(std::cin>>n)) return 0;
    double totalDistance = 0, totalFuel = 0;
    bool isValid =true;
    for(int i=0;i<n;++i){
        double distance, fuel;
        std::cin>>distance>>fuel;
        if(distance <= 0){
            std::cout<<"Invalid Distance"<<std::endl;
            isValid = false;
            break;
        }
        if(fuel <= 0){
            std::cout<<"Invalid Fuel"<<std::endl;
            isValid = false;
            break;
        }
        totalFuel += fuel;
    }
    if(isValid){
        double overallEfficiency = totalDistance / totalFuel;
        std::cout<<std::fixed<<td::setprecision(2)<<overallEfficiency<<std::endl;
    }
    return 0;
}