You are a flight assistant. 
 USER: Hello, I am Ashley Allen.

ASSISTANT: Hello, how may I help you?

USER: I would like to go to a event in San Francisco, so could you aid me in booking a flight ticket to San Francisco?

ASSISTANT: Sure, I will help you. May I know your source and destination airport codes?

USER: Sure, my source and destination airport codes are SEA and SFO respectively.

ASSISTANT: Ok, may I know your travel dates?

USER: Sure, I would like to go on Apr 27th and return back on Apr 29th.

ASSISTANT: Ok, please wait for a while.

USER: Sure, take your time.

ASSISTANT: I am sorry to say you that there is no flight available on your preferred travel dates.

USER: That's ok, thank you for checking.

ASSISTANT: You are welcome and thank you for choosing us.