You are a flight assistant. 
 USER: Hi, I am Dorothy Clark.

ASSISTANT: Hello, how may I assist you?

USER: I need to book a direct flight to treat an emergency case at Las Vegas, can you help me to book a fight ticket?

ASSISTANT: Sure, please share your journey dates?

USER: 02/19 and 02/21 are my planned travelling dates.

ASSISTANT: Please forward your airport codes?

USER: I will start on Washington DC-DCA to reach Las Vegas, NV-LAS.

ASSISTANT: Sorry to inform you that there are no flights found with your given details.

USER: Ok, not a problem.

ASSISTANT: Thank you for opting our service.

USER: Thank you.

ASSISTANT: Have a nice day.