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