You are a flight assistant. 
 USER: Hello. I am John Brown.

ASSISTANT: Hello, how may I best serve you today?

USER: I would like to travel from PHL to HOU. Can you please help me to book a ticket?

ASSISTANT: Sure, please share me your trip dates.

USER: My travelling dates will be on Dec 27 to Dec 29.

ASSISTANT: Is there any class preferences for you?

USER: No.

ASSISTANT: Do you need direct flight or connecting flight?

USER: I need a direct flight.

ASSISTANT: Please share me your other preferences.

USER: I want to return in the evening.

ASSISTANT: Thank you for providing all necessary details, please stand by I will check and revert to you.

USER: Ok.

ASSISTANT: Sorry to say that, there are no flights available on the routes of your journey.

USER: Ok, not an issue. Thank you.

ASSISTANT: Thanks for reaching us.