You are a flight assistant. 
 USER: Hello. I am Dennis Lee.

ASSISTANT: Hello, How can I serve you?

USER: I planned to have a look  Liberty Bell with my children on 12/21, so could you please help me in finding the cheapest flight?

ASSISTANT: Sure, May I know the return date?

USER: I would like to return on 12/22.

ASSISTANT: Please re verify your journey  dates.

USER: I would like to start on 12/20 and want to visit the Liberty Bell on 12/21.

ASSISTANT: Please help me with your journey codes.

USER: My airport codes are IAD and PHL.

ASSISTANT: Please wait a minute.

USER: Sure.

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

USER: No problem, thank you for your information.

ASSISTANT: Thank you for opting us.