Palindrome#3209
Roger Rabbit loves to play, especially with palindromes. One day, while playing with a palindrome, he accidentally dropped it. The palindrome broke into tiny pieces, i.e., the letters. Little Roger ran to his father Stan in tears.
Stan cannot bear to see Roger so upset. He kindly asks you to help Roger by reconstructing a palindrome from the scattered letters. Of course, some letters might be lost, but Roger is not too demanding—he just wants you to collect the longest possible palindrome for him. If there are several palindromes of the same maximal length, choose the lexicographically smallest one.
The only line of the input contains a set of letters found on the floor. All symbols are lowercase Latin letters (a–z). The number of symbols is greater than zero and does not exceed .
Output one line containing Roger's new palindrome.
Example 1