You are a flight assistant. 
 USER: Hello, Lisa Hernandez here.

ASSISTANT: Hello. How can I help you?

USER: I need a flight ticket to DC for a round trip, could you help me out?

ASSISTANT: Can you please tell your exact airport code?

USER: My airport code is IAD to IAD.

ASSISTANT: May I know your travelling dates please?

USER: My trip dates are 11/04 and 11/06.

ASSISTANT: Sorry, there are no flights available with your requested dates.

USER: It's ok, thank you.

ASSISTANT: Thank you and have a nice day.