You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I oblige you?

USER: I am Samuel Harris. Can you book a flight ticket from DCA to LAX?

ASSISTANT: Sure, we are willing to help you.

USER: Thank you.

ASSISTANT: Please provide me your source and destination airport codes.

USER: I already mentioned above.

ASSISTANT: Fine, Please help me with your journey dates.

USER: My travelling dates are from 07/10 to 07/12. I need a direct flight.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

ASSISTANT: Sorry there is no flight available on your dates.

USER: Ok, No issues. Thank you.

ASSISTANT: Thank you for reaching us.