You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you today?

USER: I would like to attend a grand event held at Washington, please help me in booking a ticket from San Francisco.

ASSISTANT: Sure, I can help you.

USER: Thank you.

ASSISTANT: Can I know your travelling dates?

USER: My planned travel dates are on Mar 27 and Mar 29.

ASSISTANT: Do you need any break?

USER: No, I want to travel in a direct flight.

ASSISTANT: May I know your airport codes to book a flight ticket?

USER: My origin and destination airport codes are SFO and DCA.

ASSISTANT: Let me know your name?

USER: My name is Samuel Nelson.

ASSISTANT: Ok, wait for some time.

USER: Sure, take your time.

ASSISTANT: Thanks for waiting there are no flights found on your details.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thanks for approaching us.