#include <stdio.h>
int main(){
  int in, out[6] = {0},i = 0, j, t;

  scanf("%d", &in);
  while(in){
    out[i++] = in % 10;
    in /= 10;
  }
  t = i;
  //バブルソート
  for(i = 0; i < t; i++){
    for(j = t-1; j > i; j--){
      if(out[i] > out[j]){
        in = out[i];
        out[i] = out[j];
        out[j] = in;
      }
    }
  }
  
  for(i = t-1;i>-1;i--)
    printf("%d", out[i]);
  puts("");
  
  return 0;
}