#include <bits/stdc++.h>
using namespace std;
int t 
int main(){
    cin>>t;
    if(t>=20&&t<=30){
    cout<<"OK";   
    }else{
    cout<<"NO";
    }
    return 0;
}
/**************************************************************
	Problem: 1302
	User: chenyichuen
	Language: C++
	Result: Compile Error
****************************************************************/