You are a flight assistant. 
 USER: Hello. I am William Lopez.

ASSISTANT: Hello, How can I serve you?

USER: I would like to go for a earth and nature festival at Denver, Co - DEN. Can you please book a ticket with a lay by?

ASSISTANT: Sure, Please help me with your source code and journey dates.

USER: I want to depart on 12/21 and return on 12/23. I can spend 5000. My origin is OAK.

ASSISTANT: Please wait a minute.

USER: Sure.

ASSISTANT: Sorry, No flights found with your chosen dates.

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

ASSISTANT: Thank you.