#include <bits/stdc++.h>
using namespace std;
int main()
{
int t;
cin>>t;
if(t>=20&&t<=30)
cout<<"OK";
else
cout<<"NO";

	return 0;
}

/**************************************************************
	Problem: 1302
	User: wqc123
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/