You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, do you need any help from us?

USER: Please book a ticket on Apr 2 to Apr 4 to attend Sports festival.

ASSISTANT: Sure, could you please share your location airport codes?

USER: My source is Denver, DEN and destination is Las Vegas, LAS.

ASSISTANT: Ok, could I have your name please?

USER: I am David Turner.

ASSISTANT: Ok, do you have any other specifications?

USER: I want a direct flight.

ASSISTANT: Sorry, there is no flight on your requested travelling dates.

USER: Ok, Thank you.

ASSISTANT: You are welcome, have a great day.