https://purengom.com/2010/08/01/%ed%96%85%ed%8b%b1-2%ec%99%80-%ea%b0%a4%eb%9f%ad%ec%8b%9c-s%eb%a5%bc-%eb%b3%b4%eb%a9%b4%ec%84%9c-%eb%93%9c%eb%8a%94-%ec%82%bc%ec%84%b1%ec%a0%84%ec%9e%90%ec%97%90-%eb%8c%80%ed%95%9c-%ec%b6%a9%ea%b3%a0/