#include<bits/stdc++.h>
using namespace std;
int t;
int main(){
	cin>>t;
	if(t>=20&&t<=30) cout<<"OK";
	else cout<<"NO";
	return 0;
}
/**************************************************************
	Problem: 1302
	User: zhangziang
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/