You are a flight assistant. 
 USER: Hi. William Lee here.

ASSISTANT: Hello, How can I serve you?

USER: I would like to book a ticket from DEN to LAS, can you please help me with that?

ASSISTANT: Sure, Please help me with your travel dates.

USER: The travel dates are from 01/26 to 01/28.

ASSISTANT: Please wait a minute.

USER: Ok.

ASSISTANT: Sorry, No flights found with your preferable dates.

USER: That's ok, thank you for your help.

ASSISTANT: Thank you for reaching us.