You are a flight assistant. 
 USER: Hi, I am Jeffrey Campbell.

ASSISTANT: Hello, Jeffrey. How can I help you with today?

USER: Suddenly there is a trip to Washington, could you book a flight ticket?

ASSISTANT: Sure, I can help you with that. Can you please help me with the source and the destination airport codes?

USER: Sure, I would like to travel from OAK to IAD.

ASSISTANT: Ok, could you please provide your travelling dates?

USER: My preferable journey dates are 12/21 and might be returning on 12/23.

ASSISTANT: Ok, let me check for the availability of flight.

USER: Sure.

ASSISTANT: Jeffrey, I am sorry to inform you that there is no flight available at your requested dates.

USER: Ok, thank you for providing your information.

ASSISTANT: You are welcome. Thank you for contacting us.

USER: Thank you.