It's first come, first served. 선착순

It's first come, first served.

선착순. (FCFS) https://en.wikipedia.org/wiki/First-come,_first-served

3 people wanted for sale. It's first come, first served.
세일에 3명 구해요. 선착순 입니다.

이것에 대한 뉴스도 한번 읽어 보세요!
http://www.bbc.com/news/magazine-34153628