#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c;
	float h,p;
	cin>>a>>b>>c;
	h=a+b+c;
	p=h/3
	printf("%.1lf",p);
} 
/**************************************************************
	Problem: 1602
	User: huxuanchen
	Language: C++
	Result: Compile Error
****************************************************************/