#include<bits/stdc++.h>
using namespace std;
int main()
{
	int t;
	cin>>t;
	if(t<20||t>30)
	cout<<"NO";
	else cout<<"OK";
	return 0;
}

/**************************************************************
	Problem: 1302
	User: ccf
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/