You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Barbara Davis.

ASSISTANT: How may I assist you Davis?

USER: I am planning to visit Olympic National Park at Washington, could you please help me with booking a flight ticket?

ASSISTANT: Sure, I will help you in booking. Can I know on what dates you are willing to travel?

USER: I would like to take off on 07/26 and return on 07/28.

ASSISTANT: May I know your preferred airport codes please?

USER: My nearest source airport code is OAK and destination airport code is DCA.

ASSISTANT: Please wait a while, I will check and inform you.

USER: Sure, take your time.

ASSISTANT: As per your requested dates there is no flight available on your desired route.

USER: That's ok, I will find an another alternate way to complete my trip. Anyways, thank you for the information.

ASSISTANT: Thank you for choosing us. Have a great day.