#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  char a[100];
  cin >> s;
  int j = 0;
  for (int i = 0; i < s.length(); i++) {
    if (s[i] != '+') {
      a[j] = s[i];
      j++;
    }
  }
  sort(a, a + j);
  for (int i = 0; i < j; i++) {
    if (i == j - 1)
      cout << a[i] << endl;
    else
      cout << a[i] << "+";
  }
  return 0;
}
