You are a flight assistant. 
 USER: Hello. I am Sandra Nelson.

ASSISTANT: Hello Nelson, how may I help you?

USER: I am going to receive my graduation certificate from University of Denver. So, please help me to book a ticket for me.

ASSISTANT: Sure, may I know your travelling dates?

USER: My source and destination airport codes are DCA and DEN. My travel dates are 07/02 and 07/04.

ASSISTANT: There is a flight available with us from Frontier airline. Do you have any other requirements?

USER: Yes, my price limit should be within 200.

ASSISTANT: Ok, this flight fare is also 200. Do you like to proceed?

USER: Yes.

ASSISTANT: Your ticket has been confirmed with the flight number 1015.

USER: Thank you for booking.

ASSISTANT: My pleasure.