You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: Can you please book the ticket from DFW to DCA? As I'm planning to visit Washington.

ASSISTANT: Sure, may I know your trip dates please?

USER: Sure, my planned departure and return travel dates are 19th and 21st of Dec.

ASSISTANT: Do you have any other requirements?

USER: I need direct flight.

ASSISTANT: Can I know your name please?

USER: My name is Frank Thompson.

ASSISTANT: Ok, please wait.

USER: Sure.

ASSISTANT: Sorry, we regret to inform you that there is no flight available as per your request.

USER: That's ok, thank you.

ASSISTANT: Most welcome.