#include<bits/stdc++.h>
using namespace std;
int main(){  
	float q;
	int y,s,x;
    scanf("%d %d %d",&y,&s,&x);
    q=(y+s+x)/3.0;
    printf("%.3f",q);
}  
/**************************************************************
	Problem: 1957
	User: chenyichuen
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2076 kb
****************************************************************/