You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you today?

USER: I want to book a direct flight to Washington, IAD to go for Holiday trip. Can you please help me for booking?

ASSISTANT: Sure, can you share me your travelling dates?

USER: My travelling dates are Dec 27 and Dec 29.

ASSISTANT: Please mention your source code.

USER: My source is Houston, HOU.

ASSISTANT: Do you have any class preference?

USER: I prefer economy class.

ASSISTANT: Is there any other specifications?

USER: No.

ASSISTANT: May I know your name please.

USER: Sure, I am Richard Martin.

ASSISTANT: Sorry, no flights are found on your travelling dates.

USER: Ok, no issues. Thank you.

ASSISTANT: Thank you for opting us.