You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Dorothy Rodriguez.

ASSISTANT: How can I help you?

USER: I need to visit Washington to meet my cousin, can you please help me to book a flight ticket from LAS to IAD?

ASSISTANT: Can I know your travelling dates?

USER: Sure, my journey dates are Apr 16 and Apr 18.

ASSISTANT: Do you have any preference?

USER: My class preference is economy.

ASSISTANT: Sorry, no flights found for your travelling dates.

USER: No problem, thank you for your information.

ASSISTANT: Thank you.