You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: Will you please help me to book a flight ticket from DEN to LGA?

ASSISTANT: Sure, may I know the travelling dates?

USER: I will start on May, 10 and return on May, 12.

ASSISTANT: Do you have any connection limit?

USER: I would prefer single connection.

ASSISTANT: Are there any other requirements?

USER: My depart time should be at evening.

ASSISTANT: May I know your name?

USER: Richard Lee.

ASSISTANT: Sorry, no flights found with your chosen dates.

USER: Not a problem, thank you for the information.

ASSISTANT: Thank you for opting us.