You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how can I serve you today?

USER: Please book a ticket from Dallas & Fort Worth, TX-DFW to Washington DC-IAD.

ASSISTANT: Ok, I can book a ticket for you. May I know your depart and arrival dates?

USER: Depart is on 12/19. Return date is 12/21.

ASSISTANT: Ok, wait a minute.

USER: Sure.

ASSISTANT: May I know your name please?

USER: I am Jack Brown.

ASSISTANT: Sorry, no flights are available for you to your desired locations.

USER: Thank you.

ASSISTANT: Thanks for communicating with us, have a nice day.