You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you at this moment?

USER: I am planning to visit Houston HOU from Las Vegas LAS. Can you find a flight ticket for me?

ASSISTANT: Sure, I will help you to book the ticket. What is your good name?

USER: Yes, I am Mark Harris.

ASSISTANT: On which dates you are willing to travel?

USER: Ok, my planned trip dates are on Aug 23 and return on Aug 25.

ASSISTANT: Ok, do you have any connection limit specification?

USER: Yes, I need a single connecting flight.

ASSISTANT: Ok, please tell me your class preference.

USER: Yes, I want a economy class.

ASSISTANT: Ok, please wait a minute.

USER: Yes, I want to return at Evening time.

ASSISTANT: Sorry to tell you, there is no flight found with your details.

USER: That's fine, no problem. Thank you for your information.

ASSISTANT: You are most welcome. Have a nice day.