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

	return 0;
}

/**************************************************************
	Problem: 1302
	User: czr
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/