You are a flight assistant. 
 USER: Hello, I am Donna Roberts.

ASSISTANT: Hello, how can I help you?

USER: I am planning to surprise my sister on her birthday at San Francisco, can you please help me in booking?

ASSISTANT: Sure, I will help you. Please share me your travelling dates?

USER: I want to travel on 12/12 and return on 12/14.

ASSISTANT: Do you have any specifications?

USER: I need a direct flight. Price limit is 1000.

ASSISTANT: Can I know your airport codes?

USER: My airport code is CA-SFO and it is a round trip.

ASSISTANT: Please wait for few minutes.

USER: Ok.

ASSISTANT: There is no flight with your requirement.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for reaching us.