#include<bits/stdc++.h> 
using namespace std;
int main(){
	int a,b,c;
	float s;
	cin>>a>>b>>c;
	s=(a+b+c)/3.0;
	printf("%.3f",s);
}	
/**************************************************************
	Problem: 1957
	User: sucongyi
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/