#include<bits/stdc++.h>
using namespace std;
int main(){ ;
	int a,b,c;
	double z;
	scanf("%d %d %d",&a,&b,&c);
	z=(a+b+c)/3.0;
	printf("%.3f",z);
}
/**************************************************************
	Problem: 1957
	User: tonghuatao123
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2076 kb
****************************************************************/