#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
    int n;
    cin>>n;
    double d,f,totalD = 0,totalF = 0;
    for(int i=0;i<n;i++){
        cin>>d>f;
        if(d<=0){
            cout<<"Invalid Distance";
            return 0;
        }
        if(f<=0){
            cout<<"Invalid Fuel";
            return 0;
        }
        totalD += d;
        totalF += f;
    }
    cout<<fixed<<setprecision(2)<<(totalD/totalF);
    return 0;
}