https://purengom.com/2008/08/28/%ec%9d%bc%eb%b3%b8%ec%9d%98-%ec%82%ac%eb%a1%80%eb%a1%9c-%eb%b3%b8%eb%8b%a4-%ec%84%af%eb%b6%80%eb%a5%b8-%ea%b3%b5%ea%b8%b0%ec%97%85-%eb%af%bc%ec%98%81%ed%99%94%eb%8a%94-%ec%9e%ac%ec%95%99/