import java.util.Arrays;
import java.util.Scanner;

public class Yukicoder256 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        char[] c =  sc.next().toCharArray();
        char d;
        Arrays.sort(c);
        for (int i = 0; i < c.length / 2; i++) {
            d = c[i];
            c[i] = c[c.length-i-1];
            c[c.length-i-1] = d;
        }
        System.out.println(c);
    }
}