You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: Mark Lee is my name. Can you help me in booking a direct flight to DFW to give a seminar?

ASSISTANT: Sure, can I know your preferable dates?

USER: My preferable dates are 05/26 and 05/28.

ASSISTANT: Ok, let me know your source code please?

USER: Los Angeles, LAX is the source code.

ASSISTANT: Sorry Lee, there are no flights found on given dates.

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

ASSISTANT: Thank you for reaching us.