#include <bits/stdc++.h>
using namespace std;
int main(){int t;  
cin>>t;
if(20<=t&&t<=30)cout<<"OK";
else cout<<"NO";
	return 0;
	}
/**************************************************************
	Problem: 1302
	User: lyy002
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/