You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I aid you today?

USER: I am David Davis want to visit Houston, can you book a ticket from DCA to HOU?

ASSISTANT: Sure, I am here to help you with that, May I know your travelling dates?

USER: Sure, my travelling dates will be 03/05 and 03/07.

ASSISTANT: Ok, wait for a minute. Sorry to say that, there are no flight's available based on your travelling dates.

USER: Ok.\. That's ok, thank you.

ASSISTANT: Thank you for reaching us.