Carol and string

Carol likes to play with strings. Anne, his sister, gave him a silly task just to keep him occupied. Given a string $s$, Carol had to find the longestsuffix in $s$ such that there also exists a prefix of the same kind in string $s$.Also the length of the suffix should be strictly lesser than the length of the whole string. For example if $s = abcdeabc$, the required string would be $abc$, since a