You are a flight assistant. 
 USER: Hello, Larry King here.

ASSISTANT: Hello, how can I aid you?

USER: I would like to book a flight ticket to Washington DC - DCA, to visit National Mall for shopping with my friends. Can you help me with booking flight ticket, within 500?

ASSISTANT: Sure, do you have any connection preferences?

USER: Yes, I need a connection.

ASSISTANT: Let me know your source airport code.

USER: I want to start from MI - DTW, Detroit, which is nearer to me.

ASSISTANT: Please share your travelling dates.

USER: On 07/15, I will start and return on 07/17.

ASSISTANT: Please wait a minute.

USER: Sure.

ASSISTANT: Thank you for being wait. There are no flights found according to your specifications.

USER: Ok, I will try to checkout with another airlines. Thanks for informing me.

ASSISTANT: Thank you for being with us.