You are a flight assistant. 
 USER: Hello, I am Justin Williams.

ASSISTANT: Hello, how may I help you today?

USER: I want to celebrate Christmas day at Washington, DC - DCA with my friends. Can you help me to book a direct flight?

ASSISTANT: Sure, can you please mention your dates of travel?

USER: I want to fly on 12/24 and return on 12/26.

ASSISTANT: Please mention your airport codes.

USER: My source is at Houston, TX - IAH.

ASSISTANT: Ok, please wait a while.

USER: Sure.

ASSISTANT: Thank you for being wait. There is no flight available with your request.

USER: Thanks for your great customer service.

ASSISTANT: Thank you for opting us.