You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

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

ASSISTANT: Sure, may I know your trip dates please?

USER: I prefer to travel on Feb 20 and Feb 22.

ASSISTANT: Do you have any other requirements?

USER: I prefer to travel in a connecting flight.

ASSISTANT: Can I know your name please?

USER: I am Joshua Hall.

ASSISTANT: Sorry, we regret to inform you that there is no flight available as per your request.

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

ASSISTANT: Most welcome.