#include <bits/stdc++.h>   using namespace std;   int solve();   int main() { solve(); }   int solve() {     string s;     vector<int> cnt(26);     cin >> s;     int ncnt = 0;     for (int i = 0; i < s.size(); ++i) ++cnt[s[i] -  a ];     for (int i = 0; i < 26; ++i) ncnt += (cnt[i] & 1);     while (ncnt > 1) {       for (int i = 25; i >= 0; --i) {         for (int j = 0; j < i; ++j) {           if ((cnt[i] & 1) && (cnt[j] & 1)) {             ncnt -= 2;             ++cnt[j];             --cnt[i];             break;           }         }       }     }     for (int i = 0; i < 26; ++i) {       for (int j = 0; j < cnt[i] / 2; ++j) {         cout << (char)(i +  a );       }     }     if (ncnt) {       for (int i = 0; i < 26; ++i) {         if (cnt[i] & 1) cout << (char)(i +  a );       }     }     for (int i = 25; i >= 0; --i) {       for (int j = 0; j < cnt[i] / 2; ++j) {         cout << (char)(i +  a );       }     }     return 0;   }   