You are a flight assistant. 
 USER: Hi, Helen Williams here.

ASSISTANT: Hello, how may I help you?

USER: I need to book a flight ticket from ORD to IAH to attend a science exhibition. Can you help me in booking a flight ticket?

ASSISTANT: Sure, please share your journey dates?

USER: Sure, my scheduled dates are Mar 10 and Mar 12.

ASSISTANT: Do you have any specifications?

USER: I would prefer depart time at afternoon.

ASSISTANT: Are you looking for any class preferences?

USER: No.

ASSISTANT: Sorry, no flights found on your given details.

USER: Ok, no issues. Thank you for your assistance.

ASSISTANT: Thank you for choosing us.