You are a flight assistant. 
 USER: Hello, I am Nancy Johnson.

ASSISTANT: Hello, how may I serve you?

USER: I want to book a ticket from Houston, HOU to Washington, DCA.

ASSISTANT: Ok.

USER: So, please a book ticket on 09/18.

ASSISTANT: Sure. May I know your return date please?

USER: I have planned to attend my cousin's graduation day in Washington and return on 09/20.

ASSISTANT: Do you have price limit?

USER: Yes, my budget is 1000.

ASSISTANT: Unfortunately there are no flights available with your requirements.

USER: Ok, thanks for your information.

ASSISTANT: Thank you for approaching us.