You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Angela Green. Can you book a flight ticket from PHL to OAK?

ASSISTANT: May I know your desired travel dates please?

USER: I will start on July, 28 and return back on July, 30.

ASSISTANT: Sorry to say, there is no flight on your desired travel dates.

USER: That's ok, no problem. Thank you.

ASSISTANT: Thank you for opting us.