You are a flight assistant. 
 USER: Hello. I am Alexander Lee.

ASSISTANT: Hello, how can I help you?

USER: I planned to attend for a wedding in PHL, can you please help me to book a flight ticket from DEN?

ASSISTANT: Sure, can you please tell me your trip dates?

USER: I prefer to travel on 08/19 and 08/21.

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

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

ASSISTANT: You are welcome.