`color(#FFFFFFff)(H)color(#E7E7E7ff)(o)color(#CFCFCFff)(r)color(#B7B7B7ff)(i)color(#9F9F9Fff)(z)color(#878787ff)(o)color(#6F6F6Fff)(n)`

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

string f(string s) {
    map<char, int> mp;
    for (char c:s) mp[c]++;

    int d = 0, p = 0;
    for (auto i:mp)
        if (i.second % 2 != 0) {
            d++;
            p = i.first;
        }

    if (d > 1) return "-1";

    string s1 = "";
    for (auto i:mp) s1 += string(i.second / 2, i.first);

    sort(s1.begin(), s1.end());

    string s2 = s1;
    reverse(s2.begin(), s2.end());

    if (d == 1)
        return s1 + p + s2;
    else
        return s1 + s2;
}

int main() {
    string s; cin >> s;
    cout << f(s);
}