You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, How can I best serve you today?

USER: Could you please help me to book a flight ticket from OAK to LAS?

ASSISTANT: Sure, can you please mention your depart and arrival dates of your journey?

USER: My travelling dates are Dec 21 and Dec 23.

ASSISTANT: Do you like to go with a connecting or direct flight?

USER: I am comfortable with any flight.

ASSISTANT: May I know if you prefer to have any other comforts in your journey?

USER: I prefer an economy class and normal cost airline.

ASSISTANT: Can I know your good name to proceed further?

USER: I am William Miller.

ASSISTANT: Sorry, no flights are available in this route as per your requested dates.

USER: Not a problem, thank you for the information.

ASSISTANT: Thank you for choosing us.