Longest Palindrome

Given a string, your task is to determine the longest palindromic substring of the string. For example, the longest palindrome in aybabtu is bab.

Input

The only input line contains a string of length n. Each character is one of a–z.

Output

Print the longest palindrome in the string. If there are several solutions, you may print any of them.

Constraints

$1 \le n \le 10^6$

Example

Input

aybabtu

Output

bab