You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Brian Miller.

ASSISTANT: How may I assist you today?

USER: I want to book a flight from IAD to PHX, can you please help me?

ASSISTANT: May I know your travelling dates, please?

USER: I will start on 19th May and will return back on 21st May.

ASSISTANT: Do you need any specifications for this reservation?

USER: Yes, I want to return in the afternoon and please choose business class.

ASSISTANT: Please wait a moment.

USER: Sure.

ASSISTANT: Sorry, there are no flight tickets available on your journey dates.

USER: No problem, thank you.

ASSISTANT: Thank you for reaching our service.