You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Justin Martinez.

ASSISTANT: I'm happy to help you, Martinez.

USER: I am planning to visit my brothers home, due to some impotent work . I want to go from DCA to OAK, can you help me out?

ASSISTANT: Sure, please specify your dates of travel?

USER: My preferable dare are 03/14 to 03/16.

ASSISTANT: Sorry Martinez, there is no flight is available as per your request.

USER: That's fine.

ASSISTANT: Thank you for choosing us.

USER: welcome.