#include <bits/stdc++.h> 
using namespace std;
int main() {
    int a, b, c; 
    scanf("%d %d %d", &a, &b, &c);
      printf("%.3f\n", (a + b + c) / 3.0);
    return 0;
}
/**************************************************************
	Problem: 1957
	User: fuhoubin
	Language: C
	Result: Compile Error
****************************************************************/