// editor3
#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];
    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;
}
}