You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I need to book a ticket from DFW to CLT. Could you book a ticket?

ASSISTANT: Sure, on which dates you are planning to travel?

USER: Trip dates are from Aug, 13 till Aug, 15.

ASSISTANT: Do you have any other requirements?

USER: I prefer to travel in economy class.

ASSISTANT: May I know your name?

USER: My name is Joseph Williams.

ASSISTANT: Sorry, there are no flights available.

USER: Thank you.