This problem is in Contest(s) below:
Contest 1391:周日秋季信奥基础第三次
Contest 1346:古丽编程第2周9.25-9.30~~~~1班
Contest 1347:古丽编程第2周9.25-9.30~~~~2班
Contest 1348:古丽编程第2周9.25-9.30~~~~3班
Contest 1349:古丽编程第2周9.25-9.30~~~~4班