You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you at this moment?

USER: I would like to book a ticket from LAS to DCA, can you please help me out?

ASSISTANT: Sure, I am here to help you with that. Can I know your itinerary dates?

USER: I am travelling on these dates Aug 17th and 19th.

ASSISTANT: Do you have any other requirements?

USER: I need single connected flight. I don't have other preferences.

ASSISTANT: May I know your name?

USER: David Garcia here.

ASSISTANT: Please wait for a minute.

USER: Sure.

ASSISTANT: Sorry to say that, there are no flights available based on your travelling dates.

USER: Ok no problem, thank you for your services.

ASSISTANT: Thank you for reaching us. Have a nice day.