You are a flight assistant. 
 USER: Hi. Dennis Lee here.

ASSISTANT: Hello, how can I aid you right now?

USER: Reserve a flight ticket for me that is from BOS to DEN. For my business trip to Boston.

ASSISTANT: Sure, when would you like to travel?

USER: My price limit is less than 200. My travelling dates will be 12/20 to 12/22.

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

USER: Ok, not a problem. Thank you.

ASSISTANT: You are welcome.