#include <bits/stdc++.h>
using namespace std;
int main(){
	int t;
	cin>>t;
	if(t>= 20 && t <=30){
	cout<<"OK";	
	}else{
    cout<<"NO";
	}
	return 0;
	
}
/**************************************************************
	Problem: 1302
	User: huanghao
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/