You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I want to book the flight ticket from IAD to LGA. Can you please help me?

ASSISTANT: May I know your desired travel dates please?

USER: My travel dates are Feb 20 and Feb 22.

ASSISTANT: Do you have any specifications?

USER: I would like to travel in the afternoon.

ASSISTANT: May I know your name please?

USER: Susan Clark.

ASSISTANT: Sorry to say, there is no flight on your desired travel dates.

USER: Ok, thank you for the information.

ASSISTANT: Thank you for opting us.