#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
    int n;
    double 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;
}