#include <bits/stdc++.h>
using namespace std;

int main() {
	string s; cin >> s;
    int n = s.size();
    vector<int>v(26);
    for(char c : s)
    {
        v[c - 'a']++;
        if(v[c - 'a'] > (n+1)/2)
        {
            cout << -1;
            return 0;
        }
    }
    vector<char> ans(n);
    int remaining = n;
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < 26; j++) {
        if (i > 0 && 'a' + j == ans[i - 1]) continue;
        bool b = true;
        for (int k = 0; k < 26; k++) {
          if ((k == j && v[k] - 1 > remaining / 2) || (k != j && v[k] > remaining / 2)) {
            b = false;
          }
        }
        if (b && v[j] > 0) {
          ans[i] = 'a' + j;
          v[j]--;
          remaining--;
          break;
        }
      }
    }

    for (int i = 0; i < n; i++) cout << ans[i];
}