#include<iostream> 
#include<cstdio>
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: Accepted
	Time:7 ms
	Memory:2076 kb
****************************************************************/