You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, How can I help you?

USER: I need your help to book a flight from DCA to SFO.

ASSISTANT: Sure, May I know your travelling dates?

USER: Sure, I want to travel on May 19 and need to return on May 21.

ASSISTANT: Do you have any connection limit?

USER: Yes, I need a flight with single connection.

ASSISTANT: Any other preferences?

USER: No.

ASSISTANT: May I know your name?

USER: Anna Phillips here.

ASSISTANT: Sorry, there are no flights found with your details.

USER: Ok, not an issue. Thank you for the information.

ASSISTANT: Thank you.