CF335B Palindrome

Given a string $ s $ , determine if it contains any palindrome of length exactly $ 100 $ as a subsequence. If it has any, print any one of them. If it doesn't have any, print a palindrome that is a subsequence of $ s $ and is as long as possible.

The only line of the input contains one string $ s $ of length $ n $ ( $ 1

If $ s $ contains a palindrome of length exactly $ 100 $ as a subsequence, print any palindrome of length $ 100 $ which is a subsequence of $ s $ . If $ s $ doesn't contain any palindromes of length exactly $ 100 $ , print a palindrome that is a subsequence of $ s $ and is as long as possible. If there exists multiple answers, you are allowed to print any of them.

A subsequence of a string is a string that can be derived from it by deleting some characters without changing the order of the remaining characters. A palindrome is a string that reads the same forward or backward.