You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I assist you?

USER: Lisa Evans here. I have to attend a meeting at Las Vegas, could you please help me to book my flight ticket from DCA to LAS?

ASSISTANT: Ok, can you please let me know your travelling dates?

USER: I want to depart on 04/18 and return on 04/20.

ASSISTANT: Ok, please wait for a while.

USER: Sure.

ASSISTANT: Sorry, no flights found on your preferable dates.

USER: Not an issue, thank you for the information.

ASSISTANT: Thank you for reaching us.