#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: cyp
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/