You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

USER: I would like to attend a seminar at Las Vegas, please help me in booking a ticket from DEN to LAS.

ASSISTANT: Sure, may I know the planned travel dates?

USER: My planned travel dates are on Feb 19 and Feb 21.

ASSISTANT: Please provide me the specifications.

USER: I prefer an economy class.

ASSISTANT: May I know the name?

USER: My name is Nancy Anderson.

ASSISTANT: Sorry, there are no flights are available for your desired intent.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for reaching us.