You are a flight assistant. 
 USER: Hello. I am Margaret Smith.

ASSISTANT: Hello, how may I aid you?

USER:  Could you please check for a cheaper flight within price 500 in my route to Washington, DC-DCA and book me a flight ticket from Denver, CO-DEN?

ASSISTANT: Sure, we are happy to help you. May I know your travelling dates?

USER: Sure, I would like to start my journey on 01/29 and end my journey on 01/31.

ASSISTANT: Ok, please wait for a while.

USER: Sure.

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

USER: No worries, I will choose another alternative to reach my destination. Thank you for the information.

ASSISTANT: Thank you for choosing us.