有n（最大20）个人围成一圈，顺序排号。从第1个人开始报数（从1到3报数），凡报到3的人退出圈子，问最后留下的是原来第几号-With n (maximum 20) individuals form a circle, the order Arranging. 1 person reported from the start number (number from 1 to 3 report), 3 registration people who withdraw from the circle