#include<iostream>
using namespace std;

class worker{
    protected:
    int dur,calo;
};
class fit:public worker{
    public:
    void calo(int logs){
        int totaldur=0,totalcalo=0;
        
        for(int i=0;i<logs;i++){
            cin>>dur>>calo;
            
            if(dur<=0||calo<=0){
                cout<<"Invalid input";
                return;
            }
            totaldur+=dur;
            totalcalo+=calo;
        }
        double average=(double)totalcalo/totaldur;
        cout<<average;
    }
};
int main(){
    string usertype,userid;
    string goal;
    int logs;
    
    cin>>usertype>>userid;
    cin>>goal>>logs;
    fit f;
    f.cal(logs)
    return 0;
}