#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n>=20&&n<=30) cout<<"OK";
	else cout<<"NO";	
	return 0;
}
/**************************************************************
	Problem: 1302
	User: chenjunlin
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/