#include<bits/stdc++.h>
using namespace std;
int main(){ 
	int t;
	cin>>t;
	if(t>=20&&t<=30){
		cout<<"OK";
	}else{
		cout<<"NO";
	}
}
/**************************************************************
	Problem: 1302
	User: sucongyi
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/