You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: I am Frank Young. I am planning on travelling to LAS to meet my cousin, can you please help me to book a flight ticket from DFW?

ASSISTANT: May I know your desired travel dates please?

USER: My trip dates are May 16 to May 18.

ASSISTANT: Do you have any other specifications?

USER: I need a connecting flight which depart and return in evening.

ASSISTANT: Sorry to say, there is no flight on your desired travel dates.

USER: No issue, thank you.

ASSISTANT: Thank you for opting us.