You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I am Katherine Collins. I have to report in Boston medical on 02/11, can you hold me a flight ticket?

ASSISTANT: Sure, I will search a flight for you. May I know your return date?

USER: I should return on 02/13.

ASSISTANT: Ok, could you let me know your airport codes?

USER: I want to start from Washington DC - DCA and return from Boston, MA - BOS.

ASSISTANT: Do you want any other requirements to fulfil?

USER: My price range is 5000.

ASSISTANT: Ok, let me check the flight availability.

USER: Sure.

ASSISTANT: I apologize to say that, there are no flights available today.

USER: Ok, not a problem. Thanks for your response.

ASSISTANT: Thank you for opting us.