You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Gregory Gonzalez here.

ASSISTANT: How can I help you?

USER: I would like to prefer a business class for my business trip to Washington. So can you book the flight ticket for me?

ASSISTANT: Can I know your airport codes?

USER: The airport codes are from LAX to DCA.

ASSISTANT: Let me know your travelling dates.

USER: My travel dates are from Oct 17 to Oct 19.

ASSISTANT: Do you have any preference?

USER: I would like to prefer a direct flight.

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

USER: Not a problem. Thank you.

ASSISTANT: Thank you.