in:

4
1 2 3 3

out:

2

可以 Hack 掉一些题解：

• https://www.luogu.com.cn/blog/prince1/solution-b2097
• https://brookstudy.blog.luogu.org/solution-b2097
• https://www.luogu.com.cn/blog/ToZero/solution-b2097