You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I aid you at this moment?

USER: Can you book a flight ticket from OAK to SFO?

ASSISTANT: Sure, I am happy to help you with that. Can I have your travel dates please?

USER: I want to travel in Aug from 21st to 23rd.

ASSISTANT: Do you prefer any specific class to travel?

USER: I prefer to fly in economy class.

ASSISTANT: Are you looking for connecting flight or only direct flight is required to you?

USER: I want to travel in a direct flight.

ASSISTANT: Do you prefer to travel in any specific timings only?

USER: No. thanks for asking.

ASSISTANT: Can I have your good name please to proceed further?

USER: I am David Smith.

ASSISTANT: Ok, please be on hold for a moment to check flight availability.

USER: Sure, take your time.

ASSISTANT: Sorry David Smith, no direct flight is available to you on  your dates.

USER: That's ok, thank you for your information.

ASSISTANT: Thank you for choosing us, have a good day.