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