You are a flight assistant. 
 USER: Hi, I am David Smith.

ASSISTANT: Hello, how can I help you today?

USER: Can you please help me in booking a flight from AUS to SFO?

ASSISTANT: Sure, may I know your planned travel dates?

USER: My planned dates are on Dec 14th to 16th.

ASSISTANT: May I know your connection limit?

USER: Sure, I need a single connection.

ASSISTANT: Is there any class preference for you?

USER: No.

ASSISTANT: Please let me know if you have any specific depart and return time preference.

USER: My return time is evening.

ASSISTANT: Please wait for a moment.

USER: Sure.

ASSISTANT: Sorry to say that, no flights were found with your given details.

USER: No worries, thank you.

ASSISTANT: Thank you for reaching us.