You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: Please help me to book a flight ticket from IAD to BOS.

ASSISTANT: Sure, may I know the travelling dates?

USER: Aug, 21 and Aug, 23 are my travelling dates.

ASSISTANT: Do you have any connection limit?

USER: I would prefer single connection.

ASSISTANT: Is there any other requirements?

USER: No.

ASSISTANT: May I know your name?

USER: Karen Johnson.

ASSISTANT: Please wait a minute.

USER: Sure.

ASSISTANT: Sorry, no flights found with your chosen dates.

USER: That's ok, thank you for the information.

ASSISTANT: Thank you for opting us.