#include<bits/stdc++.h> 
using namespace std;
int main()
{
   double j;
   int x,y,n;
   cin>>x>>y>>n;
   j=(x+y+n)/3.0;
   printf("%.3f",j);
}
/**************************************************************
	Problem: 1957
	User: yangjunwen
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/