// compile: make data
// run: ./data < data.in
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#ifdef LOCAL
#include <debug/codeforces.h>
#define debug(x...) _debug_print(#x, x);
#define Debug(x...) _debug_print_format(#x, x);
std::ifstream terminal("/dev/tty");
#define PP cerr<<"\033[1;30mpause...\e[0m",terminal.ignore();
#else
#define debug(x...)
#define Debug(x...)
#define PP
#endif
template<typename...Args> void print_(Args...args){((cout<<args<<" "),...)<<endl;}
#define rep(i,a,b) for(int i=(a);i<(int)(b);++i)
#define sz(v) ((int)(v).size())
#define print(...) print_(__VA_ARGS__);
#define FIND(a, x) ((find(a.begin(),a.end(),(x))!=a.end())?1:0)
#define cmin(x,...) x=min({(x),__VA_ARGS__})
#define cmax(x,...) x=max({(x),__VA_ARGS__})
#define INTMAX (int)(9223372036854775807)
#define INF (int)(1152921504606846976)
#define NaN (int)(0x8b88e1d0595d51d1)
#define double long double
#define int long long
#define uint unsigned long long
#define MAXN 200010

int32_t main() {
    ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);

    string s; cin >> s;
    vector<int> a(26, 0);
    for (auto &c: s) ++a[c - 'A'];
    string res = "";
    int lst = -1;
    rep(i, 0, sz(s)) {
        int mx = 0, mxid = 0, rem = sz(s) - i;
        rep(j, 0, 26) if (a[j] > mx) mx = a[j], mxid = j;
        if (mx > ceil(rem / 2.0)) {
            cout << -1 << endl;
            return 0;
        }
        // debug(mx, mxid, rem, a)
        // PP
        if (rem & 1 && mx == ceil(rem / 2.0)) res += (char)('A' + mxid), --a[mxid], lst = mxid;
        else {
            rep(j, 0, 26) if (a[j] && j != lst) {
                res += (char)('A' + j), --a[j];
                lst = j;
                break;
            }
        }
    }
    cout << res << endl;

    return 0;
}