import java.util.ArrayList;
 
  /**
     A system of voice mail boxes.
  */
public class MailSystem
{
    /**
       Constructs a mail system with a given number of mailboxes
       @param mailboxCount the number of mailboxes
    */
  public MailSystem(int mailboxCount)
    {
      mailboxes = new ArrayList<Mailbox>();
 
        // Initialize mail boxes.
 
      for (int i = 0; i < mailboxCount; i++)
      {
        String passcode = "" + (i + 1);
        String greeting = "You have reached mailbox " + (i + 1)
          + ". \nPlease leave a message now.";
        mailboxes.add(new Mailbox(passcode, greeting));
      }
    }
 
    /**
       Locate a mailbox.
       @param ext the extension number
       @return the mailbox or null if not found
    */
  public Mailbox findMailbox(String ext)
    {
      int i = Integer.parseInt(ext);
      if (1 <= i && i <= mailboxes.size())
        return mailboxes.get(i - 1);
      else return null;
    }
 
  private ArrayList<Mailbox> mailboxes;
}