You are a flight assistant. 
 USER: Hi. I am Richard Lee.

ASSISTANT: Hello, how can I aid you?

USER: I want to book a direct flight ticket to attend an emergency case. Can you help me?

ASSISTANT: Sure, can you share your trip dates?

USER: Thank you. 05/10 and 05/12 are my travelling dates.

ASSISTANT: May I know your airport codes?

USER: DFW and LAS are my airport codes.

ASSISTANT: Give me a minute.

USER: Ok.

ASSISTANT: Sorry, there is no flight on your given dates.

USER: No issue. Thank you.

ASSISTANT: Thank you for picking us.