#include<iostream>
#include<iomanip>
using namespace std;
class FuelEfficiency
{
    private:
    static double totalDistance;
    static double totalFuel;
    public:
    staic void calculate()
    {
        int n;
        cin>>n;
        totalDistance=0;
        totalFuel=0;
        for(int i=0;i<n;i++)
        {
            double d,f;
            cin>>d>>f;
            if(d<=0)
            {
                cout<<"Invalid Distance";
                return;
            }
            if(f<=0)
            {
                cout<<"Invalid Fuel";
                return;
            }
            totalDistance+=d;
            totalFuel+=f;
        }
        double efficiency=totalDistance/totalFuel;
        cout<<fixed<<setprecision(2)<<efficiency;
    }
};
double FuelEfficiency::totalDistance=0;
double FuelEfficiency::totalFuel=0;
int main()
{
    FuelEfficiency::calculate();
    return 0;
}