#include <bits/stdc++.h>
using namespace std;
int main(){
     float a,s,d,v ;
     cin>>a>>s>>d;
     v=(a+s+d)/3;
     printf("%.3f",v);
}

/**************************************************************
	Problem: 1957
	User: huangluowei
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/