You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Stephen Lee.

ASSISTANT: How can I guide you, Lee?

USER: I am planning to visit Chicago, can you please book me a ticket from DEN to ORD?

ASSISTANT: Sure, please provide me your journey dates.

USER: My planned dates of journey are from 04/21 to 04/23.

ASSISTANT: Please wait for a minute.

USER: Sure, please search for a ticket fare under 500.

ASSISTANT: There are no flights available with your preferences.

USER: Ok, not an issue. I will find any alternate for this trip. Thank you for providing information.

ASSISTANT: Thank you for contacting us.