You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Alexander Lee.

ASSISTANT: How may I assist you?

USER: I am planning to book a ticket from IAD to DTW. Can you please help me out to book a ticket for me?

ASSISTANT: Sure, I am here to help you out. May I know your travelling dates please?

USER: I would like to travel on Aug 19 and return back on Aug 21.

ASSISTANT: How much you can afford for airfare?

USER: I budget is below 500.

ASSISTANT: Alexander Lee, there are no flights available in your route.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you for reaching us.