This problem is in Contest(s) below:
Contest 1257:2016.7C高级班第12课测试
Contest 1258:2016.7C长训班第12课测试
Contest 1088:武进区第4届程序设计比赛(小学)
Contest 1629:WJOI2011
Contest 1584:2018.9长训基础班假期练习