I'm recently thinking of a problem. Given a sequence $$$a$$$, find the value of

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. Where

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the longest non-decreasing sequence of $$$a$$$ and $$$n$$$ is the length of $$$a$$$. $$$n$$$ is large to $$$10^5$$$ and $$$a_i$$$ is extremely small, only $$$20$$$? I can't think of a solution. Can anyone help me? Please.