import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		char[] b = a.toCharArray();
		Arrays.sort(b);
		String ans = "";
		for(int i=b.length-1;i>=0;i--) ans+=b[i];
		System.out.println(ans);
	}
}