You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you at this moment?

USER: I need to travel from BOS to DCA, can you help me in that?

ASSISTANT: sure, I will help you with that. Can I have your travel dates please?

USER: My trip dates are Nov 15 to 17.

ASSISTANT: Ok,  please let me know your preferable class.

USER: I am comfortable in any class.

ASSISTANT: Do you  have any other specifications?

USER: Please ensure that my depart time is in afternoon.

ASSISTANT: Can I have your good name please?

USER: Brian Phillips here.

ASSISTANT: Sorry to inform you that no flight is available to you on your planned dates.

USER: Ok, no issues. Thank you for the information.

ASSISTANT: Thank you for choosing us, have a good day.