For technical reasons, some programming languages (Kotlin, C #) will not be available during round 877. ×

B. Palindrome
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

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.

Input

The only line of the input contains one string s of length n (1 ≤ n ≤ 5·104) 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.