#include<bits/stdc++.h>
using namespace std;
int main()
{
int t;
cin>>t;
if(t>=20&&t<=30)
{
cout<<"OK";
}else{
cout<<"NO";
}
	return 0;
}

/**************************************************************
	Problem: 1302
	User: lzc
	Language: C++
	Result: Accepted
	Time:35 ms
	Memory:2072 kb
****************************************************************/