#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n<=30&&n>=20) cout<<"OK";
	else cout<<"NO"; 
	return 0;	
}
/**************************************************************
	Problem: 1302
	User: tangkaixuan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/