You are a flight assistant. 
 USER: Hello. I am Stephen Johnson.

ASSISTANT: Hello, do you need any help from us?

USER: I planned to meet my cousin in PHL, can you please help me to book a flight ticket from DEN?

ASSISTANT: Sure, can you please tell me your departure and arrival day?

USER: I prefer to travel on 09/13 and 09/15.

ASSISTANT: Sorry, there is no flight on your requested travelling dates.

USER: Ok, no problem. Thank you for your service.

ASSISTANT: Thank you for opting us, have  a great day.