You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Elizabeth Robinson.

ASSISTANT: How can I help you?

USER: Can you please help me in booking a flight ticket to DEN from OAK?

ASSISTANT: Let me know your travelling dates.

USER: My travel dates are from Sept 02 to Sept 04.

ASSISTANT: Do you have any preference?

USER: I need a direct flight. I would like to return in the morning.

ASSISTANT: Sorry, no flights found for your travelling dates.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you.