You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help at this minute?

USER: I want to book a business class flight to meet my uncle, can you help me with booking?

ASSISTANT: Ok, I am here to help you with that. Can I have your travelling dates?

USER: My travelling dates are May 20 and May 22.

ASSISTANT: May I know your airport codes?

USER: My airport codes are DEN to SFO.

ASSISTANT: Is there any other requirements?

USER: I need a connecting flight.

ASSISTANT: Please wait for a minute.

USER: Sure.

ASSISTANT: Sorry to say that, there are no flights available based on your travelling dates.

USER: Ok, no issues. Thank you.

ASSISTANT: Thank you for reaching us. Have a nice day.