You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how can I assist you for the day?

USER: I am Charles Hernandez. Can you please book a flight ticket from Denver, DEN to Boston, BOS?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: When you are willing to travel?

USER: I want to start my journey on 05/18 and return back on 05/20.

ASSISTANT: Do you have any class preference?

USER: I am comfortable with any class.

ASSISTANT: Please wait for a moment.

USER: Sure.

ASSISTANT: Sorry, we found no flights on your given dates.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for reaching us.