Rearrange to Form Palindrome

Given a string S consisting of lowercase English letters, determine if it is possible to rearrange its characters to form a palindrome. A palindrome is a string that reads the same backward as forward.

If it is possible, output a valid palindrome constructed by placing half of the occurrences of each character in order, then a middle character (if any exists), and finally the reverse of the first half. Otherwise, output IMPOSSIBLE.

For example, for the input aabb, one valid output is abba.

inputFormat

A single line of input containing a string S with only lowercase English letters.

outputFormat

If it is possible to rearrange S to form a palindrome, print the palindrome. Otherwise, print IMPOSSIBLE.## sample

aabb

abba