#include<bits/stdc++.h;
using namespace std;
int main(){
	int y,s,a,g;
	scanf("%d %d %d",&y,&s,&a);
	g=(y+s+a)/3.0;
	printf("%.3f",g)
	
}

/**************************************************************
	Problem: 1957
	User: zhengzihao3
	Language: C++
	Result: Compile Error
****************************************************************/