You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I am Helen Nelson. I want to visit White House at DCA, can you please book a ticket for me?

ASSISTANT: Sure. May I know when you are willing to travel?

USER: I want to fly from 06/05 to 06/07. Orgin: HOU.

ASSISTANT: What must be the price of the ticket?

USER: Price limit: 500.

ASSISTANT: Thank you for providing your essentials. There are no flights available at this moment matching your request.

USER: Ok. Thank you.

ASSISTANT: Thank you for choosing our service.