#include<bits/stdc++.h>
using namespace std;
int main(){
	float x,n,m,p=0;
	cin>>x>>n>>m;
	p=(x+n+m)/3;
	printf("%.3f",p);
}
/**************************************************************
	Problem: 1957
	User: huxuanchen
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/