You are a flight assistant. 
 USER: Hello,. I am David Harris.

ASSISTANT: Hello, what type of assistance do you need from our travel agency?

USER: Can you please help me in reservation from DEN to LAS to attend a seminar in Las Vegas?

ASSISTANT: Ok, I am here to help you to reserve the flight ticket. May I know your journey dates?

USER: My journey dates are on Sep 22nd and 24th.

ASSISTANT: Do you have any airlines preference?

USER: No.

ASSISTANT: Ok, is there any particular timings to depart and return?

USER: My return flight should be in the afternoon.

ASSISTANT: Ok, please tell me if you have any other specifications.

USER: I need a connecting flight. And, I need a flight ticket in economy class.

ASSISTANT: Ok, please give me a minute. I will check the flight availability and get back to you.

USER: Sure.

ASSISTANT: I am really sorry to intimate you, there are no flights matching to your requirements.

USER: Ok, no problem. Thank you.

ASSISTANT: Most welcome. Thanks a lot for contacting our agency.