You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Thomas Lee. Please help me to book a flight ticket in my preferable travel dates Sept, 26 and Sept, 28.

ASSISTANT: Do you need any halt in between your journey?

USER: No, I need a direct flight.

ASSISTANT: Sure, may I know your respective airports codes please?

USER: My airport codes are DEN and IAH.

ASSISTANT: Sorry, there is no direct flight for you on your route.

USER: That's ok, no problem.

ASSISTANT: Thanks for choosing us, have a nice day.

USER: Welcome.