#include<bits/stdc++.h>
using namespace std;
int main(){
   int a,b,c;
   cin>>a>>b>>c;
   cout<<fixed<<setprecision(3)<<(a + b +c) / 3.0 <<endl; 

	return 0;
}


/**************************************************************
	Problem: 1957
	User: admin
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/