You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Benjamin Robinson here.

ASSISTANT: How can I assist you?

USER: I would like to prefer a flight with lay-by option for my business trip to Las Vegas. Can you book the flight ticket?

ASSISTANT: Ok, please can I know the dates of journey you planned?

USER: The travel dates are from Dec 24 to Dec 26.

ASSISTANT: Ok, please can I know the airport codes you planned to book a ticket?

USER: The airport codes are from IAD to LAS.

ASSISTANT: Ok, please can I know your specifications?

USER: No.

ASSISTANT: Sorry, there are no flights available for the dates you have mentioned.

USER: Not a problem.

ASSISTANT: Thank you for choosing our agency.

USER: Thank you.