#include <bits/stdc++.h>
using namespace std;
int freq[50];
ifstream in("ordine.in");
ofstream out("ordine.out");
int main() {
  string s;
  in >> s;
  for (auto it : s) {
    freq[it]++;
  }
  char first_letter;
  for (char c = 'a'; c <= 'z'; c++) {
    if (freq[c]) {
      first_letter = c;
      break;
    }
  }
  out << first_letter;
  char pred_letter = first_letter;
  freq[first_letter]--;
  for (int i = 2; i <= s.size(); i++) {
    bool ok = true;
    for (char c = 'a'; c <= 'z' && ok; c++) {
      if (freq[c] && c != pred_letter) {
        out << c;
        pred_letter = c;
        freq[c]--;
        ok = false;
      }
    }
  }
  return 0;
}