You are a flight assistant. 
 USER: Hello, I am Lisa Martinez.

ASSISTANT: Hello. How can I help you today?

USER: can you please aid me in booking a ticket in a flight which is going from DEN to DCA?

ASSISTANT: Sure, I am glad to help you in booking. Can you please share your travel dates?

USER: Sure, I would like to go on 11/19 and return back on 11/21.

ASSISTANT: Please wait a moment.

USER: Ok, ensure it is a direct flight.

ASSISTANT: Thank you for waiting. Sorry, no flights are available on your planning dates.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for reaching us.

USER: Welcome.