#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: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/