#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;
using P = pair< int, int >;

string t = "abcdfgjhijklm";
int a[14];

int main() {
    string s;
    cin >> s;
    rep(i, s.size()) {
        a[s[i]-'a']++;
    }

    bool two=false;
    bool zero=false;
    bool ok=true;
    rep(i, 13) {
        if (a[i] == 2) {
            if (!two) { two = true; }
            else { ok = false; break; }
        }
        else if (a[i] == 0) {
            if (!zero) { zero = true; }
            else { ok = false; break; }
        }
        else if (a[i] > 2) {
            ok = false;
            break;
        }
    }

    if (!ok) { cout << "Impossible" << endl; }
    else {

        if (zero) {
            rep(i, 13) {
                if (a[i] == 0) {
                    cout << char('a' + i) << endl;
                    return 0;
                }
            }
        }
        else {
            rep(i, 13) {
                cout << char('a'+i) << endl;
            }
        }

    }

}