You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello. How may I assist you today?

USER: Please could you book a ticket from Boston, MA-BOS to Denver, CO-DEN.

ASSISTANT: May I know your travelling dates to search a flight?

USER: Sure. Start date is 11/19 and will return by 11/21.

ASSISTANT: May I know your name to proceed further?

USER: I am Debra Green.

ASSISTANT: Sorry, I could not find any flight with your travel dates.

USER: Thanks.

ASSISTANT: My pleasure.