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