#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c;
	double p=0;
	scanf ("%d %d %d",&a,&b,&c);
	p=(a+b+c)/3.0;
	printf ("%.3f",p);
	return 0;
}
/**************************************************************
	Problem: 1957
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2076 kb
****************************************************************/