#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: dengyuanyan
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/