You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: I want to book a direct flight to San Francisco, can you help me?

ASSISTANT: Sure, can you please tell me your airport codes?

USER: My airport codes are from LAX to SFO.

ASSISTANT: Ok, may I know your name please?

USER: Myself Brian Harris.

ASSISTANT: Ok, may I know your travelling dates?

USER: My travel dates are 08/18 and 08/20.

ASSISTANT: Brian, all flight tickets are sold out in your planned month.

USER: No problem, thanks for your information.

ASSISTANT: My pleasure.