You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Rebecca Mitchell here.

ASSISTANT: Rebecca Mitchell, how can I render you today?

USER: Please help me out in booking the ticket from DEN to LAS.

ASSISTANT: Sure, I am here to help you. May I know your travel dates please?

USER: My trip dates will be Oct 25 to Oct 27.

ASSISTANT: Ok, hold on for a moment. Let me check the best available flight for you.

USER: Ok.

ASSISTANT: Sorry Rebecca Mitchell, there are no flights available on your requested dates.

USER: That's ok. Thank you.

ASSISTANT: Welcome, thank you for choosing us. Have a great day.