You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you today?

USER: I am looking to book a flight ticket from DCA to DEN. Can you help me for that?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: May I know your travel dates please?

USER: My travelling dates are Apr 15 and Apr 17.

ASSISTANT: Ok, do you have any specifications?

USER: I prefer to book a single connecting flight.

ASSISTANT: May I know your name please?

USER: My name is Katherine Lopez.

ASSISTANT: Sorry Katherine Lopez, there are no flights available on your requested dates.

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

ASSISTANT: Welcome, thank you for choosing us. Have a great day.

USER: Welcome.