You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Robert Parker here.

ASSISTANT:  Robert Parker, how may I assist you today?

USER: I would like to travel DCA for attending client meeting over there. Please, assist me to book a flight ticket from DEN.

ASSISTANT: Sure, I can assist you with that. May I know your dates of travel?

USER: Ok, my travelling dates are from 07/19 to 07/21.

ASSISTANT: Please wait for while, let me check  for the flights availability.

USER: Sure.

ASSISTANT: Sorry to say that, there are no flights available on your route as per your given travel dates.

USER: Ok, no problem. Thank you for your help.

ASSISTANT: Thank you for reaching us, have a great day.