根据字符串求最大回文字符串，怎么用C语言的程序的编写的代码的过程去实现字符串的构造

Question

Problem Description
Given a string, you use some letters or digits to creat a new string, this new string have three properties.
1. any two adjacent letter aren't the same.
2. the new string have the biggest length.
3. the new string have the biggest lexicographical ordering.

Input
The input consists of multiple test cases. Each test case contain a string, the string is consist of 'a'~'z', 'A' - 'Z' and '0' - '9'. the length of string is not exceed 500.

Output
For each case, print the new string.

Sample Input
2
abaa
001

Sample Output
aba
010