#include <iostream>
using namespace std;

int main()
{
	int t;
	cin >> t;
	if (20 <= t && t <= 30)
	{
		cout << "OK";
	}
	else
	{
		cout << "NO";
	}
}
/**************************************************************
	Problem: 1302
	User: xiaomingze
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/