#include<iostream>
#include<iomanip>
using namespace std;
class workout
{
    public:
    void display(int arr[],int n)
    {
        double cal=0;
        double min=0;
        for(int i=0;i<(n*2);i++)
        {
            if(i%2==0)
            {
                min+=arr[i];
            }
            else
            {
                cal+=arr[i];
            }
        }
        cout<<fixed<<setprecision(2)<<cal/min<<endl;
    }
};
int main()
string type;
string id;
string goal;
int n;
cin>>type>>id>>goal>>n;
int arr[n*2];
for(int i=0;i<(n*2);i++)
{
    cin>>arr[i];
    if(arr[i]<=0)
    {
        cout<<"Invalid input";
        return 0;
    }
}
workout obj;
obj.display(arr,n);
return 0;
}