You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

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

ASSISTANT: Sure, may I know your trip dates?

USER: Thank you. I have planned my travel dates as June 16 and June 18.

ASSISTANT: Do you have any other requirements?

USER: I would prefer direct flight so please check with that.

ASSISTANT: Can I know your name please?

USER: Sure, myself Mark Garcia.

ASSISTANT: Sorry, we regret to inform you that there is no flight available as per your request.

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

ASSISTANT: Most welcome.