#include<bits/stdc++.h>

using namespace std;

int main() {
  string s;
  cin >> s;
  vector<int> v;
  for (auto ch : s) {
    if(ch != '+') {
      v.push_back(ch - 48);
    }
  }
  sort(v.begin(), v.end());
  for(int i = 0; i < v.size(); i++) {
    if(i == v.size() - 1) {
      cout << v[i];
    }
    else {
      cout << v[i] << "+";
    }
  }
  cout << '\n';
}