You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Margaret Lewis.

ASSISTANT: How may I guide you today?

USER: Could you please help me to reserve a flight ticket from New York to Denver?

ASSISTANT: Sure, I am glad to help you with that. Can you please provide your preferable dates of travelling?

USER: Thank you, my planned trip dates are Apr 15th and 17th.

ASSISTANT: May I know your origin and destination airport codes for booking?

USER: The origin and destination airport codes are LGA and DEN.

ASSISTANT: Please wait a moment to check the flights on your route.

USER: Ok, please make sure that the returning time is afternoon.

ASSISTANT: We regret to inform you that there are no flights moving to your region with your planned dates of travelling.

USER: It's ok, not a problem with that. I will choose some other source to travel. Anyways thank you for your time.

ASSISTANT: Thank you for reaching us, have a great day.