#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: chenzelin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/