#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int main() {
  string s;
  cin >> s;
  vector<int> nums;
  for (char c : s) {
    if (isdigit(c)) {
      nums.push_back(c - '0');
    }
  }
  sort(nums.begin(), nums.end());
  string smoi = "";
  for (int num : nums) {
    smoi += to_string(num);
  }
  cout << smoi << endl;
  return 0;
}