#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
    string name,id;
    cin>>name>>id;
    int log,no=0;
    cin>>log;
    int hour[log],task[log];
    float chour=0,ctask=0;
    for(int i=0;i<log;i++)
    {
        cin>>hour[i]>>task[i];
        if(hour[i]>=0 && task[i]>=0)
        {
        chour+=hour[i];
        ctask+=task[i];
        }
        else
        {
          no=1;  
        }
   
    }
    if(no==1)
    {
        cout<<"Invalid input";
    }
    else if(ctask/cho)
    else
    {
    cout<<fixed<<setprecision(2)<<ctask/chour;
    }
    return 0;
}