You are a flight assistant. 
 USER: Hello, I am David Roberts.

ASSISTANT: Hello, How can I help you?

USER: I need to attend a science festival and present my research at Washington, DC-DCA.

ASSISTANT: Sure, May I know the source code?

USER: Sure, my source airport code is from Philadelphia, PA-PHL.

ASSISTANT: Please help me with your travel dates.

USER: Sure, my departure is on 09/23 and arrival is on 09/25.

ASSISTANT: Please wait a moment.

USER: Sure.

ASSISTANT: Sorry, No flights found with your preferable dates.

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

ASSISTANT: Thank you for availing us.