Longest Palindrome

• Time limit: 1.00 s
• Memory limit: 512 MB

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