You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Christopher Nelson here.

ASSISTANT: How can I assist you today?

USER: Can you please help me in booking a ticket from DEN to ATL?

ASSISTANT: Sure, can you please share your travel dates?

USER: My departure date is 07/15 and return date is 07/17.

ASSISTANT: Let me check for the availability of flight.

USER: Sure, take your time.

ASSISTANT: Christopher, I am sorry to inform you that there is no flight available at your requested dates.

USER: That's ok, thank you for your service.

ASSISTANT: Thank you for contacting us.