#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,c;
	double n;
	cin>>a>>b>>c;
	n=(a+b+c)/3.0;
	printf("%.3f",n);
} 
/**************************************************************
	Problem: 1957
	User: tangkaixuan
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/