You are a flight assistant. 
 USER: Hello, I am Lisa Baker.

ASSISTANT: Hello, how may I assist you today?

USER: I want to celebrate Christmas with my family at Denver, Can you book a ticket on 12/25?

ASSISTANT: Sure, May I know your return day and airport codes of your journey?

USER: My return date is on 12/27. My destination is CO - DEN. I would like to travel from Houston, TX - IAH.

ASSISTANT: Thank you for details provided. Please wait a moment, I will check and get you back with the best.

USER: Sure.

ASSISTANT: Thank you for waiting, We are sorry to inform you that there were no flights available with your given data.

USER: Thank you for providing information.

ASSISTANT: Thank you for choosing us, Have a nice day ahead.