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

• \(1 \leq n \leq 10 ^ 6\)

Example

Sample input

aybabtu

Sample output

bab