You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello,. How can I help you today?

USER: My name is Sandra Mitchell. Can you please book a flight ticket to Oakland, CA-OAK, to attend my grandmother's 50th birthday.

ASSISTANT: Sure. Let me know your origin point and travelling dates?

USER: Ok, my origin point is Washington, DC-IAD. The dates are 02/16 and 02/18.

ASSISTANT: Ok. Wait for a moment I will check and revert you back.

USER: Ok.

ASSISTANT: Thanks for your time. Unfortunately, There is no flight with your specified dates.

USER: Ok, no issue.

ASSISTANT: Thank you for choosing us.

USER: Thank you for your service.