#include <iostream>
#include <iomanip>
using namespace std;
int main(){
    int n;
    doubloe d,f,td=0,tf=0;
    if(!(cin>>n||n<=0)){
        return 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;
        }
        td+=d;
        tf+=f;
    }
    double overallEfficiency+td/tf;
    cout<<fixed<<setprecision(2)<<overallEfficiency<<"\n";
    return 0;
}