#include<bits/stdc++.h>
using namespace std;
int main(){
	
	int n;
	cin>>n;
	if(n>20&&n<30){
		cout<<"OK";
	}else{
		cout<<"NO";
	}
	
	return 0;
}
/**************************************************************
	Problem: 1302
	User: huangyaojie3
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/