You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I aid you today?

USER: Can you help me to book a flight from PHL to DEN?

ASSISTANT: Sure, when would you like to travel?

USER: My trip dates are June 23 and 25.

ASSISTANT: May I know your name please?

USER: David Williams here.

ASSISTANT: Do you have any preferences?

USER: I prefer to travel in business class.

ASSISTANT: Sorry, no flights were available at this moment.

USER: Ok, thank you.

ASSISTANT: Thank you for reaching us.