You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Michael Collins here.

ASSISTANT: How may I assist you?

USER: I would like to visit Dallas, please book a ticket from DCA to DFW.

ASSISTANT: Sure, let me know your travel dates please?

USER: My planned travel dates are on May 18 and May 20.

ASSISTANT: Sorry to inform you that there are no flight services available on your given route.

USER: Ok, no issues. Thank you for your information.

ASSISTANT: Thanks for reaching us.