You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I guide you at this moment?

USER: I am Mark Davis. Can you please book a flight ticket from LAX to SFO?

ASSISTANT: Sure, I am really happy to help you to book the ticket. Can you please let me know your travel dates?

USER: Sure, I need to travel on dates of Jan 17 and Jan 19.

ASSISTANT: Ok, please give a minute. In the meanwhile, tell me if you have any requirements?

USER: I would like to travel in economy class.

ASSISTANT: Sorry to inform you that, there is no flight found in this route on the dates you have given.

USER: Oh! It is sad to hear. Anyway, thank you for your time.

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