https://blog.wongcw.com/2019/01/15/%e5%93%88%e5%9b%89%e5%87%ba%e8%a1%8c%e4%bc%b0%e5%80%bc50%e5%84%84%e7%be%8e%e5%85%83%e6%9a%ab%e7%84%a1ipo%e6%99%82%e9%96%93%e8%a1%a8/