You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I amend you?

USER: Katherine Lopez here, I would like to book a ticket from DCA to SFO. Can you please help me to book a ticket?

ASSISTANT: Sure, how much do you want to spend on your ticket?

USER: My travelling dates will be on 04/15 to 04/17. Fare is 500.

ASSISTANT: Ok, please wait for a moment.

USER: Ok.

ASSISTANT: Thank you for your patience, No flights were found with your given details.

USER: Not an issue, thank you.

ASSISTANT: Thank you for opting us.