You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Lisa Mitchell here.

ASSISTANT: How can I assist you today?

USER: Book a ticket from DEN to LAS.

ASSISTANT: Sure, will you mention your travelling dates please?

USER: My trip starts on 09/20 and 09/22.

ASSISTANT: Please give me a moment.

USER: Sure.

ASSISTANT: There is no flights found under your preferable details.

USER: It's ok, thanks for your information.

ASSISTANT: Welcome, have a great day.