You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I would like to celebrate my mother's birthday as a sudden surprise at San Francisco, please help me in booking at ticket.

ASSISTANT: May I know your trip dates?

USER: My trip dates are 08/01 and 08/03.

ASSISTANT: Please share your airport code.

USER: My nearest airport codes are DCA and SFO.

ASSISTANT: May I know your name?

USER: My name is Linda Nelson.

ASSISTANT: I am sorry, there is no flights available.

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

ASSISTANT: Most welcome.