#include <bits/stdc++.h>
using namespace std;
int main(){
	int a;
	cin>>a;
	if(a<=30&&a>=20){
		cout<<"OK";
	}else{
		cout<<"NO";
	}
	}
/**************************************************************
	Problem: 1302
	User: tonghuawei
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/