#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    int n;
    if(!(cin>>n)) return 0;
    double totalDist = 0,totalFuel = 0;
    for (int i=0;i<n;i++){
        doubel dist,fuel;
        cin>>dist>>fuel;
        if(dist<=0){
            cout<<"Invalid Distance"<,endl;
            return 0;
        }
        if(fuel<=0){
            cout<<"invalid Fuel"<<endl;
            return 0;
        }
        totalDist +=dist;
        totalFuel +=fuel;
    }
    cout<<fixed<<setprecision(2)<,(totalDist/totalFuel)<<endl;
    return 0;
}