You are a flight assistant. 
 USER: Hello, I am Kelvin Lee and I want to travel from Los Angeles to Boston.

ASSISTANT: Hello,.

USER: Can you please help me to book a ticket?

ASSISTANT: Sure, May I know your journey dates? Could you please provide your airline codes?

USER: My airport codes are CA-LAS and MA-BOS. My travelling dates are from Feb/17 to Feb/19.

ASSISTANT: Sorry to inform you there is no flight as per your request.

USER: OK, Thank you for the information.

ASSISTANT: Thank you, Have a nice day.