You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: This is Robert Edwards from Washington. I am planning to visit Yosemite adventure with my college friend's in IAD, will you please assist me in booking a flight ticket from DCA?

ASSISTANT: Your travelling dates please?

USER: My depart will be on July 17th and return on July 19th.

ASSISTANT: Ok, please wait.

USER: Sure, but I will prefer to travel in business class.

ASSISTANT: Sorry, no flights found to reserve your ticket in business class.

USER: Ok, not an issue. Thank you for your information.

ASSISTANT: Most welcome.