You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

USER: I am Donald Martinez from Denver. My cousin has invited me to attend his birthday party at Boston. Can you help me in booking a ticket from Denver?

ASSISTANT: Please help me with your airport codes.

USER: The source and destination airport codes are DEN and BOS respectively.

ASSISTANT: Can I have your trip dates please?

USER: I am planning my journey on 06/30 and return on 07/02.

ASSISTANT: Please hold on a moment.

USER: Ok, make sure the price is below 200.

ASSISTANT: Donald, no flights has been found on your request.

USER: Its ok, thank you for the information.

ASSISTANT: Thank you for approaching us.