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