#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: 1987
	User: zhangyilei
	Language: C++
	Result: Wrong Answer
****************************************************************/