You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you at this moment?

USER: I am planning to visit Detroit, can you please book me a ticket from DCA to DTW?

ASSISTANT: Sure, I am here to help you with that. Can I know your planned trip dates?

USER: My planned dates of journey are Mar 21 and Mar 23.

ASSISTANT: Do you have any other requirements?

USER: I prefer to depart in the evening flight.

ASSISTANT: May I know your name?

USER: My name is Gary Hill.

ASSISTANT: Do you have any class preference?

USER: No.

ASSISTANT: Sorry to say that, there is no flight available based on your travelling dates.

USER: Ok, not an issue. Thank you for providing information.

ASSISTANT: Thank you for reaching us.