#include<iostream>
#include<iomanip>
using namespace std;
class workout{
    public:
    void dispaly(int arr[],int n){
        double cal = 4;
        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;
}