https://soooprmx.com/python101-005-%ed%95%a8%ec%88%98%eb%aa%a8%eb%93%88-%ea%b7%b8%eb%a6%ac%ea%b3%a0-%eb%8f%84%ec%9b%80%ec%9d%b4-%eb%90%98%eb%8a%94-%eb%8f%84%ea%b5%ac%eb%93%a4/