You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: My name is David Perez. I want to travel from Atlanta to Los Angeles for a business trip.Can you please help me for booking the ticket?

ASSISTANT: Can you provide me your preferable dates?

USER: My departure date is 01/19 and return date is 01/21.

ASSISTANT: Sorry David, I don't have any flight with your source and destination.

USER: Ok, thanks for your help.

ASSISTANT: You are most welcome.