You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: My name is Sandra Clark. I would like to visit Philadelphia. Can you help me for booking a flight ticket from LAS to PHL?

ASSISTANT: Can I know your travelling dates?

USER: My travelling dates are Dec 11 and Dec 13.

ASSISTANT: Do you have any preference?

USER: I need a direct flight.

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

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

ASSISTANT: Thanks.