You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Can you aid me to book a flight ticket from IAD to DFW?

ASSISTANT: May I know your travelling dates?

USER: I planned my trip on the dates May 20 and May 22.

ASSISTANT: Do you have any preference?

USER: I prefer afternoon at the time of depart and morning flight for my return journey.

ASSISTANT: Can I know your name?

USER: Myself Betty Evans.

ASSISTANT: I regret, there is no flight for your requirement.

USER: No issue, anyway thank you for checking.

ASSISTANT: Thank you.