import java.util.*;

public class Main {
    static final int MOD = 1000000007;
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] arr = sc.next().toCharArray();
		Arrays.sort(arr);
		StringBuilder sb = new StringBuilder();
		for (int i = arr.length - 1; i >= 0; i--) {
		    sb.append(arr[i]);
		}
		System.out.println(sb);
   }

}