#include<bits/stdc++.h>
using namespace std;

int main(){
	int t;
	cin>>t;
	if(20<=t<=30){
		cout<<"OK";
	}else{
		cout<<"NO";
	}
	
}

/**************************************************************
	Problem: 1302
	User: linzihang
	Language: C++
	Result: Wrong Answer
****************************************************************/