#include <bits/stdc++.h>
using namespace std;
int main() {
  int a[105], n;
  char s[105];
  scanf("%s", s);
  for (int i = 0, j = 0; i < strlen(s); i += 2, j++) a[j] = s[i] - 48, n = j;
  n++;
  sort(a, a + n);
  for (int i = 0; i < n - 1; i++) printf("%d+", a[i]);
  printf("%d", a[n - 1]);
  return 0;
}
