Smallest Lexicographical String

Given a string s consisting of lowercase English letters, you are allowed to perform the following operation any number of times:

• Select any contiguous substring of s with even length (i.e. its length ℓ satisfies \( \ell\ \%\ 2 = 0 \)), and reverse it.

Your task is to determine the lexicographically smallest string that can be obtained by applying this operation repeatedly. A string a is lexicographically smaller than a string b if at the first position where they differ, the character in a comes before the corresponding character in b in the alphabet. It can be proven that the lexicographically smallest string obtainable by these operations is equivalent to the string with its characters sorted in non-decreasing order.

Input/Output Requirements: The solution should read input from standard input (stdin) and output the result to standard output (stdout).

Examples:

Input:  abcd
Output: abcd
Input:  dcba
Output: abcd

</p>

inputFormat

The input consists of a single line containing a string s of lowercase English letters.

outputFormat

Output a single line containing the lexicographically smallest string that can be obtained.

## sample

abcd

abcd