#include<bits/stdc++.h>
using namespace std;
int main(){
	int t;
	cin>>t;
	if(20<=t<=30){
	cout<<"OK";
    }
	else{
	cout<<"NO";                  
    }
	
	
	
	
	
	
	return 0;
	
	
	
	
	
	}
/**************************************************************
	Problem: 1302
	User: zhangchenhao
	Language: C++
	Result: Wrong Answer
****************************************************************/