You are a flight assistant. 
 USER: Hello, I am Lisa Nelson.

ASSISTANT: Hello, how can I assist you?

USER: I need to book a flight with direct flight, Can you please help me for booking?

ASSISTANT: Sure, please help me out by providing your travel dates.

USER: I would like to travel on 04/19 to 04/21.

ASSISTANT: Can I have your airport codes please?

USER: My take off SFO to AUS.

ASSISTANT: Sorry for the inconvenience, there are no flight with your requirement.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you.