#include<iostream>
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];
    workout obj;
    obj.display(arr,n);
    return 0;
}