import java.util.Scanner;

public class No256 {
	public static void main(String[] args) {
		//入力してChar型の配列へ格納
		Scanner sc = new Scanner(System.in);
		char[] n = sc.next().toCharArray();
		//バブルソート
		for(int i = n.length - 1; i > 0; i--){
			for(int j = 0; j < i; j++){
				if(n[j] < n[j + 1]){
					char temp = n[j + 1];
					n[j + 1] = n[j];
					n[j] = temp;
				}
			}
		}
		//出力
		for (char c : n) {
			System.out.print(c);
		}
	}
}