https://purengom.com/2008/05/18/%ed%95%9c%ea%b5%ad-%ec%a2%85%ec%9d%b4-%ec%8b%a0%eb%ac%b8%ec%9d%b4-%ec%82%b4%ea%b8%b8%ec%9d%80-%ec%9d%bd%ea%b8%b0-%ec%89%ac%ec%9b%80-%eb%bf%90/