You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am David Parker, Could you help me to make a reservation from DCA to ORD?

ASSISTANT: Sure, may I know your planned travel dates?

USER: My travelling dates are on 04/19 and 04/21.

ASSISTANT: Sorry, there are no flights found with your given dates.

USER: Ok, thank you.

ASSISTANT: Thank you for opting us.