You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am David Lopez.

ASSISTANT: How can I assist you today?

USER: I planned to attend for a meeting in ORD, can you please help me to book a flight ticket from LAS?

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

USER: I prefer to travel on Mar 4 and Mar 6.

ASSISTANT: Do you have any class preference?

USER: No.

ASSISTANT: David Lopez, I am sorry to inform you that there is no flight available at your requested dates.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for contacting us.