input: Write a python function to classify emails as "Junk" or "Not Junk" based on specific patterns in the content.
  assert classify_email("Limited time offer! Buy now!") == "Junk"
  assert classify_email("Meeting at 3 PM tomorrow") == "Not Junk"
  assert classify_email("Order now to get a 50% discount") == "Junk"
  assert classify_email("Hello, just checking in.") == "Not Junk"
output: def classify_email(email):
      junk_keywords = ["offer", "buy now", "order now", "discount"]
      for keyword in junk_keywords:
          if keyword.lower() in email.lower():
              return "Junk"
      return "Not Junk"