#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0, i##_len = (n); i < i##_len; i++)
#define reps(i, s, n) for(ll i = (s), i##_len = (n); i < i##_len; i++)
#define rrep(i, n) for(ll i = (n) - 1; i >= 0; i--)
#define rreps(i, e, n) for(ll i = (n) - 1; i >= (e); i--)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())
#define len(x) ((ll)(x).length())

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    // ifstream in("input.txt");
    // cin.rdbuf(in.rdbuf());
    string s;
    cin >> s;
    map<char, ll> cnt;
    rep(i, len(s)) cnt[s[i]]++;
    ll one = 0, two = 0;
    for(auto x : cnt) {
        if (x.second == 1) one++;
        else if (x.second == 2) two++;
        else {
            cout << "Impossible" << endl;
            return 0;
        }
    }
    if ((one == 11) && (two == 1)) {
        set<char> se;
        rep(i, 'm' - 'a' + 1) se.insert((char)('a' + i));
        for(auto x : cnt) se.erase(x.first);
        cout << (*se.begin()) << endl;
    }
    else if ((one == 13) && (two == 0)) {
        rep(i, 'm' - 'a' + 1) cout << (char)('a' + i) << endl;
    }
    else {
        cout << "Impossible" << endl;
    }
    return 0;
}