You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I want to visit Oakland for business meet, can you book a ticket?

ASSISTANT: Sure, may I know your preferable dates?

USER: My travel dates are 02/18 and 02/20.

ASSISTANT: Can you please provide me your airport codes?

USER: My airport codes are IAD to OAK. I want to book a ticket in the name of Anna Gonzalez.

ASSISTANT: Sorry for inconvenience, there is no flight available for your request.

USER: That's fine. Thank you for checking.

ASSISTANT: Thank you for your positive response.