#include<bits/stdc++.h>
using namespace std;
int main()
{
    int t;
    cin>>t;
    if(t>=20 && t<=30){
    	cout<<"OK"<<endl;
      }else{
      	cout<<"NO"<<;
      }


	return 0;
}

/**************************************************************
	Problem: 1302
	User: lbq002
	Language: C
	Result: Compile Error
****************************************************************/