You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Mark Lewis here.

ASSISTANT: How can I assist you?

USER:  Can you please help me in booking the ticket from DEN to DCA? As I need to attend a function.

ASSISTANT: Ok, may I know your travelling dates?

USER: Sure, my travelling dates are 07/27 and 07/29.

ASSISTANT: No flights found on your preferable dates to reserve your ticket.

USER: Ok, no problem. Thank you for assisting me.

ASSISTANT: Thank you for reaching us.