#include<bits/stdc++.h> 
using namespace std;
int main()
{
	int a,b,c;
	double n;
	cin>>a>>b>>c;
	n=(a+b+c)*1.0/3;
	printf("%.3f\n",n);
	return 0;
}
/**************************************************************
	Problem: 1957
	User: zhangchenyu
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/