#include <bits/stdc++.h>
int main() {
  std::string input;
  std::cin >> input;
  std::vector<int> counts(3, 0);
  for (int i = 0; i < input.size(); ++i) {
    if (input[i] == '+') {
      continue;
    } else {
      counts[input[i] - '1'] += 1;
    }
  }
  bool first = true;
  for (int i = 0; i < counts.size(); ++i) {
    for (int j = 0; j < counts[i]; ++j) {
      if (!first) {
        std::cout << "+";
      }
      std::cout << (char('1' + i));
      first = false;
    }
  }
  return 0;
}
