#include<bits/stdc++.h>
using namespace std;
int main(){
	int x,y,z;
	double p;
	scanf("%d %d %d",&x,&y,&z);
	p=(x+y+z)/3.0;
	printf("%.3f",p);
	return 0;
}
/**************************************************************
	Problem: 1957
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2076 kb
****************************************************************/