#include,iostream>
#include<iomanip>
using namespace std;
int main(){
    int n;
    cin>>n;
    double d,f;
    double td=0.0,tf=0.0;
    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 e=td/tf;
    cout<<fixed<<setprecision(2)<<e;
    return 0;
    
}