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

}

/**************************************************************
	Problem: 1302
	User: mc002
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/