Find Encrypted Password (A.K.A Compute Encoded Product Name

The input is guaranteed to be a lowercase palindrome. Rearrange all of its characters to get the lexicographically smallest password that is still a palindrome.

输入格式

One line with a lowercase palindrome of length 1..100000.

输出格式

Output the lexicographically smallest palindrome after rearrangement.

样例 1

输入：

babab

输出：

abbba

样例 2

输入：

yxxy

输出：

xyyx

样例 3

输入：

ded

输出：

ded

样例说明

Example 1: the left half is ab and the middle is b, which mirrors to abbba. Example 2: the left half is xy, giving xyyx. Example 3: the sides can only be d and the middle e, so it stays ded.