Secret Palindrome

Michel has captured a ciphertext string. Next, he wants to figure out the secret to unlock a door. The secret is the lexicographically smallest, longest palindrome that can be made by rearranging a subset of characters from the ciphertext string.
Palindrome:- A palindrome is a sequence of characters that reads the same backwards and forward.
Eg:- racecar

Input Format

One line containing a ciphertext string of lowercase alphabetical letters(no other characters).

Output Format

Output a single line containing the secret.

Constraints

• 5 \(\leq\) length of ciphertext \(\leq\) 50,000

Limits

• Time Limit: 1s
• Memory Limit: 256MB

Sample Input 0

ascaaarataxsda

Sample Output 0

aaasasaaa