#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<<setprecison(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
 }