You are a flight assistant. 
 USER: Hi, Mary Lee here.

ASSISTANT: Hello, how may I assist you today?

USER: Please look for the flights which are running on the route from CLT to DCA, can you please book a ticket for me if tickets are available?

ASSISTANT: Can you please share on what dates you are willing to travel?

USER: My preferable dates are 12/18 and 12/20.

ASSISTANT: Sorry Lee, there is no flight available with your details.

USER: Thank you for the information.

ASSISTANT: You are welcome.