#include<iostream>
#include<iomanip>
using namespace std;
class A
{
    public:
    static void display(int hr[], int task[],int n)
    {
        double hours = 0;
        double ts = 0;
        for(int i=0 ; i<n ; i++)
        {
            hours += hr[i];
            ts += task[i];
        }
        cout<<fixed<<setprecision(2)<<ts/hours;
    }
};
int main();
{
    string name,id;
    int n;
    cin>>name>>id>>n;
    int hr[n];
    int task[n];
    for(int i=0; i<n ; i++)
    {
        cin>>hr[i];
        cin>>task[i];
        if(hr[i<0]||task[i]<0 || task[i]>100)
        {
            cout<<"Invalid input";
            return 0;
        }
    }
    A::display(hr,task,n);
}