import java.util.Scanner;

class Main {
	public static void main(String[] args) throws Exception {
		Scanner in = new Scanner(System.in);
		String n = in.next();
		int h = n.length();

		int[] k = new int[h];
		for(int i=0; i<h; i++) {
			k[i] = Integer.parseInt(Character.toString(n.charAt(i)));
		}

		for(int i=0; i<h; i++) {
			for(int j=0; j<h-i; j++) {
				if(k[j+1] > k[j]) {
					int temp = k[j];
					k[j] = k[j+1];
					k[j+1] = temp;
				}
			}
		}

		String ans = "";
		for(int i=0; i<h; i++) {
			ans += String.valueOf(k[i]);
		}

		System.out.println(ans);
	}
}