You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you?

USER: I am Robert Hernandez want to visit Las Vegas on my vacation, can you book a ticket with price under 500?

ASSISTANT: Please share your itinerary dates.

USER: Sure, my travelling dates will be 05/06 and 05/08.

ASSISTANT: May I know your airport codes?

USER: Yes, I want to fly from DCA to LAS.

ASSISTANT: Please hold on for a while.

USER: Ok.

ASSISTANT: Sorry Robert, no flight is available for you.

USER: That's ok, thank you.

ASSISTANT: Thank you for contacting us.