You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you?

USER: I am Stephanie Turner want to visit Washington to meet my parents, can you help me to book a ticket within the fare of 500?

ASSISTANT: May I know your desired travel dates please?

USER: Sure, my travelling dates will be 04/18 and 04/20.

ASSISTANT: Please may I know your preferred airport code?

USER: Yes, I want to choose my source as ORD as it is near to me and my destination is DCA.

ASSISTANT: Sorry to say, there is no flight on your desired travel dates.

USER: That's ok, thank you.

ASSISTANT: Thank you for choosing us.