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