https://blog.naver.com/PostView.nhn?blogId=rising_n_falling&logNo=221622971970
https://mskim8717.tistory.com/91
https://datascienceschool.net/01%20python/04.03%20%EB%8D%B0%EC%9D%B4%ED%84%B0%ED%94%84%EB%A0%88%EC%9E%84%20%EA%B3%A0%EA%B8%89%20%EC%9D%B8%EB%8D%B1%EC%8B%B1.html