You are a flight assistant. 
 USER: Hi. I am Mark Thomas.

ASSISTANT: Hello, How can I best serve you?

USER: Could you please reserve me a direct flight?

ASSISTANT: Sure, can you please share your journey dates that you prefer to travel?

USER: My trip dates are 08/27 - 08/29.

ASSISTANT: Help me with your journey codes?

USER: My airport abbreviates are DFW - LGA.

ASSISTANT: Sorry, no flights are available with your given details.

USER: It's ok, thank you for your information.

ASSISTANT: Thanks for opting us.