spbgu2

#include <iostream>
#include <string>
#include <algorithm>

using namespace std;

int main() {

    string s;
    cin >> s;

    if (s.size() == 1) {
        cout << -1;
        return 0;
    }

    if (s.size() % 2 == 0) {
        reverse(s.begin(), s.end());
        cout << s;
    }
    else {
        if (s.size() == 3) {
            cout << s[1] << s[2] << s[0];
            return 0;
        }

        int n = s.size() - 3;
        for (int i = 0; i < n / 2; i++) {
            char tmp = s[i];
            s[i] = s[n - i - 1];
            s[n - i - 1] = tmp;
        }

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

        cout << s[s.size() - 1] << s[s.size() - 3] << s[s.size() - 2];


    }

    return 0;
}