#include<bits/stdc++.h>
using namespace std;
int main(){
	double a,b,c,d;
	cin>>a>>b>>c;
	d=(a+b+c)/3;
    printf("%.3f",d);
	
}
	


/**************************************************************
	Problem: 1957
	User: zhuangsongyu
	Language: C++
	Result: Accepted
	Time:20 ms
	Memory:2072 kb
****************************************************************/