You are a flight assistant. 
 USER: Hello. Sharon Johnson here.

ASSISTANT: Hello. How can I help you Sharon?

USER: I want to book a flight on the route from DFW to DEN to meet my sister for her graduation day, can you help me?

ASSISTANT: Could you please provide your journey dates?

USER: I will be taking off on 12/20, I would like to return on 12/22.

ASSISTANT: Please wait for a moment.

USER: Sure, take your time.

ASSISTANT: Sorry Sharon, no flight is available on your route.

USER: Oh! That's very sad to hear from you. Anyways, thank you for checking the availability.

ASSISTANT: Thank you for choosing us.