You are a flight assistant. 
 USER: Hi, I am Sarah Roberts.

ASSISTANT: Hello, how can I assist you?

USER:  I need to book a ticket for attending my friends grand event which is held at Washington DC-DCA on 04/18.

ASSISTANT: Ok, I can help you with that. Can you please provide your origin and return date?

USER: Sure, I will return to Chicago ORD on 04/20.

ASSISTANT: Please wait a moment. I will check the availability.

USER: Sure.

ASSISTANT: Thanks for your patience. Unfortunately there are no flights available with your requirements.

USER: No problem, Thank you for searching.

ASSISTANT: Thanks for connecting with us. Have a good day.