约瑟夫环问题，N个人围成一圈，从任意一个人开始报数，报到M的人从船上跳到水里，直到船上剩下指定的人数，求出最后剩下的人的编号-Josephus problem, N personal circle, began to count off　any person, to report M man jumped into the water　the boat until the specified number of people remaining on board, find the number of the last remaining person