#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(20<=n&&n<=30){
		cout<<"OK";
	}else{
		cout<<"NO";
	}
/**************************************************************
	Problem: 1302
	User: wangyiyang
	Language: C++
	Result: Compile Error
****************************************************************/