A15717 | Serval and Brain Power

Serval loves Brain Power and his brain power problem.

Serval defines that a string $T$ is powerful iff $T$ can be obtained by concatenating some string $T'$ multiple times. Formally speaking, $T$ is powerful iff there exist a string $T'$ and an integer $k\geq 2$ such that

$$ T=\underbrace{T'+T'+\dots+T'}_{k\text{ times}} $$

For example, $\texttt{gogogo}$ is powerful because it can be obtained by concatenating $\texttt{go}$ three times, but $\texttt{power}$ is not powerful.

Serval has a string $S$ consists of lowercase English letters. He is curious about the longest powerful subsequence of $S$ , and he only needs you to find out the length of it. If all the non-empty subsequences of $S$ is not powerful, the answer is considered to be $0$ .

A string $a$ is a subsequence of a string $b$ if $a$ can be obtained from $b$ by the deletion of several (possibly, zero or all) characters.

The first line contains a single string $S$ ( $|S|\leq 80$ ) consisting of lowercase English letters.

Print a single integer — the length of the longest powerful subsequence of $S$ . If all the non-empty subsequences of $S$ is not powerful, print $0$ .