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B. Palindrome

time limit per test

2 secondsmemory limit per test

256 megabytesinput

standard inputoutput

standard outputGiven 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.

Input

The only line of the input contains one string *s* of length *n* (1 ≤ *n* ≤ 5·10^{4}) containing only lowercase English letters.

Output

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.

Examples

Input

bbbabcbbb

Output

bbbcbbb

Input

rquwmzexectvnbanemsmdufrg

Output

rumenanemur

Note

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.

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