#include <bits/stdc++.h>
using namespace std;
int main(){
	int a;
	cin>>a;
	if(20<=a&&a<=30)cout<<"OK";
	else cout<<"NO";
	return 0;
}
/**************************************************************
	Problem: 1302
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/