#include <bits/stdc++.h>
int main() {
  int a = 0, b = 0, c = 0;
  char ch;
  while (ch = getchar()) {
    if (ch == '1')
      a++;
    else if (ch == '2')
      b++;
    else if (ch == '3')
      c++;
    else if (ch == '\n')
      break;
  }
  bool first = true;
  for (int i = 0; i < a; i++) {
    if (first == true) {
      printf("1");
      first = false;
    } else
      printf("+1");
  }
  for (int i = 0; i < b; i++) {
    if (first == true) {
      printf("2");
      first = false;
    } else
      printf("+2");
  }
  for (int i = 0; i < c; i++) {
    if (first == true) {
      printf("3");
      first = false;
    } else
      printf("+3");
  }
  printf("\n");
  return 0;
}
