You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how best may I serve you today?

USER: Nancy Thomas here. I'm planning to visit Houston, can you please book a ticket from DEN to HOU?

ASSISTANT: Sure, Do you require any stopovers in your journey?

USER: No, I need direct flight.

ASSISTANT: May I know on which dates you are willing to travel?

USER: Sure, my planned departure and return travel dates are 23rd and 25th of July.

ASSISTANT: Do you like to go with a economy class or business class?

USER: I'm ok with any of the classes.

ASSISTANT: We are sorry to say that, there is no direct flight found on your requested dates.

USER: Oh! That's ok, thank you giving the information.

ASSISTANT: Thanks for opting us.