You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: Karen Walker this side, I am planning for an trekking event at Philadelphia with my colleagues. can you help me to book a ticket?

ASSISTANT: Sure, may I know your airport codes please?

USER: I am going to start from OAK and return from PHL.

ASSISTANT: Ok, kindly mention your travelling dates.

USER: My travelling dates are 03/17 and 03/19.

ASSISTANT: Ok, hold on for a moment. Sorry Karen, there are no flights on your requested dates.

USER: Sure. Ok, no issues. Thank you for checking.

ASSISTANT: Thank you for choosing us, have a good day.