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Palindrome

A palindrome is a string that reads the same way both from right to left and from left to right.

A set of large Latin letters (not necessarily different) is received at the input of the program. It is allowed to rearrange letters, as well as delete some letters. It is required to make a palindrome of the largest length from these letters according to the specified rules, and if there are several such palindromes, then select the first of them in alphabetical order.

Input data

The first line of the input data contains the number $N$ (1 <= $N$ <= 100000). The second line contains a sequence of $N$ large Latin letters (the letters are written without spaces).

Output data

In a single line of output data, output the desired palindrome.

Test Groups

25 points — (1 ≤ N ≤ 10) .

25 points — (1 ≤ N ≤ 1 000 ) .

50 points — full limits.

Examples
Input data
3
AAB
Output data
ABA
Input data
6
QAZQAZ
Output data
AQZZQA
Input data
6
ABCDEF
Output data
A
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