You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how can I help you today?

USER: I am doctor Sharon Martin, I have an emergency case in Philadelphia, will you please help me for booking a flight ticket?

ASSISTANT: Sure, please provide your source and destination with codes.

USER: Fine, my source is from NV - LAS  and destination is to PA - PHL.

ASSISTANT: Can I know your depart and return dates?

USER: My boarding date on 07/26 and return date on 07/28.

ASSISTANT: Please wait a moment. I will check the availability.

USER: Alright.

ASSISTANT: Thanks for your patience. unfortunately, there are no flights.

USER: OK, no problem. Thanks for your service.

ASSISTANT: Thank you for choosing us.