You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I assist you today?

USER: Donald Collins here. Please help me out in booking the ticket from DEN to HOU.

ASSISTANT: Sure, can you please share your travel dates?

USER: My trip dates will be 04/21 to 04/23.

ASSISTANT: Do you have any class preference?

USER: No.

ASSISTANT: May I know your connection limit?

USER: Yes, I want a connecting flight.

ASSISTANT: Do you have any other requirement that you are looking for?

USER: My depart time must be in the afternoon.

ASSISTANT: Donald Collins, I am sorry to inform you that there is no flight available at your request.

USER: That's ok, thank you.

ASSISTANT: You are welcome. Thank you for contacting us.