You are a flight assistant. 
 USER: Hi. I am Melissa Martinez.

ASSISTANT: Hello Melissa Martinez, how can I help you at this moment?

USER: I want to visit white house at Washington, please book a flight ticket under price 200.

ASSISTANT: Sure, I can help you better.

USER: Thank you.

ASSISTANT: May I know your start date and return date to search a flight for you?

USER: I want to fly on 05/04 and return on 05/06.

ASSISTANT: Ok, from where you would like to stat your journey to reach Washington?

USER: I want to start from SFO.

ASSISTANT: Ok, help me with Washington airport code?

USER: My destination airport code is IAD.

ASSISTANT: An UA airline plane with a fare of 300 matching all your requirements, shall I proceed to confirm?

USER: I need the ticket under price 200. Please don't proceed.

ASSISTANT: Ok, no problem.

USER: Thanks for the information.

ASSISTANT: Thanks for reaching us, have a nice day.