This problem is in Contest(s) below:
Contest 1325:2024春周日早C++c1(塘下)
Contest 1197:2022学年第二学期实小拓展课
Contest 1235:2023暑期C++新生
Contest 1397:2025春周日下 p2
Contest 1395:2025春周六下 p2
Contest 1398:2025春周日晚p2