You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I am Ryan Martin. I want to book a flight ticket on 12/17 with a direct flight. Can you help me out in reservation?

ASSISTANT: Sure, may I know your airport codes?

USER: My airport codes are from DEN to MSP.

ASSISTANT: Can you please provide me your return date?

USER: I will be return on 12/19.

ASSISTANT: Do you have price limit?

USER: Price limit is 500.

ASSISTANT: Unfortunately there is no flight on your price limit.

USER: Ok, No problem. Thank you.

ASSISTANT: Thanks for choosing us.