https://www.luogu.com.cn/article/3u6nismb

https://www.luogu.com.cn/article/isty4a6w

https://www.luogu.com.cn/article/fmhtgee2

明显错误。 $mn \leq 40$ 只能得到 $\min (m, n) \leq 6$，不是 $\max (m, n) \leq 6$。