#include<iostream>
#include<iomanip>
int main()
{
    int n;
    cout<<fixed<<setprecision(2)<<overallEfficieny<<endl;
    if(!(std::cin>>n)) return 0;
    double totalDistance = 0.0, totalFuel = 0.0;
    double distance,fuel;
    for(int i=0;i<n;++i){
        std::cin>>distance>>fuel;
        if(distance <= 0){
            std::cout<<"Invalid Distance"<<std::endl;
            return 0;
        }
        if(fuel <= 0){
            std::cout<<"Invalid Fuel"<<std::endl;
            return 0;
        }
        totalDistance += distance;
        totalFuel += fuel;
    }
    if(totalFuel>0){
        double overallEfficiency = totalDistance / totalFuel;
        std::cout<<std::fixed<<setprecision(2)<<overallEfficiency<<endl;
    }
}