#include<iostream>
#include<iomanip>
using namespace std;
class workout {
    public:
    void display(int arr[], int n) {
        double a = 0.0;
        double b = 0.0;
        for(int i = 0; i < n*2; i++){
            if (i % 2 ==0){
                b += arr[i]; 
                
            }
            else { a += arr[i];}
            
        }
        cout<< fixed << setprecision(2) << a / b << 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;