#include<bits/stdc++.h>
using namespace std;
double a;
int main(){
	int n,m,k;
	cin>>n>>m>>k;
	a=(n+m+k+0.0)/3;
	printf("%.3f\n",a); 
}
/**************************************************************
	Problem: 1957
	User: zhengzihao
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/