https://purengom.com/2008/06/28/%eb%8f%84%ec%84%9c%ea%b4%80-%ec%a0%84%ec%9f%81-12%ed%99%94-%ec%9d%b4%ec%a0%9c-%eb%ac%b4%eb%b2%95%ec%9d%80-%ec%a7%88%ec%83%89%ec%9d%b4%eb%8b%a4/