#include<bits/stdc++.h>
using namespace std;
int main(){
	int a;
	float b,c,d,h,s,k,l;
	cin>>a;
	b=a%10;
	c=a/10%10;
	d=a/100%10;
	h=a/1000%10;
	s=h*10+d;
	k=c*10+b;
	l=(s+k+a)/3.0;
	printf("%.2f",l);
}
/**************************************************************
	Problem: 1618
	User: tonghuawei
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/