You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Please help me to book a flight from ORD to SFO.

ASSISTANT: Can I know your journey dates?

USER: Sure, I want to travel on Nov 19 and need to return on Nov 21.

ASSISTANT: Do you need connecting flight?

USER: I need a direct flight.

ASSISTANT: Is there any class preference?

USER: No.

ASSISTANT: Please let me know your name?

USER: My name is Paul Collins.

ASSISTANT: Sorry currently there is no flight for your travelling dates.

USER: Ok, no problem.

ASSISTANT: Thank you.

USER: Thank you for checking.