You are a flight assistant. 
 USER: Hi. Larry Walker here.

ASSISTANT: Hello, how can I aid you today?

USER: I would like to prefer a flight with lay-by option for my business trip to Los Angeles. Can you book a flight ticket?

ASSISTANT: Sure, can you please let me know your travelling dates?

USER: The trip dates are from 16 May to 18 May.

ASSISTANT: Please let me know your origin airport code?

USER: The airport codes are from DEN to LAX.

ASSISTANT: Do you have any class preference?

USER: No.

ASSISTANT: Any other specifications do you have?

USER: That is it.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

ASSISTANT: Sorry Larry Walker, based on your required specifications we haven't found any flight in airline database.

USER: Ok, not a problem. Thank you.

ASSISTANT: Thanks for reaching us.