You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Can you help me to book a flight ticket from IAH to DCA?

ASSISTANT: Please provide your travelling dates.

USER: My trip dates are Nov, 16 and Nov, 18.

ASSISTANT: Do you have class preference?

USER: No.

ASSISTANT: Do you have specification?

USER: I need to depart at afternoon time.

ASSISTANT: Can I know your name?

USER: Steven Perez here.

ASSISTANT: Sorry, there is no flight with your requirement.

USER: Not a problem, thank you for the information.

ASSISTANT: Thank you.