#include <bits/stdc++.h>
using namespace std;
using ll = long long;

string alpha = "abcdefghijklm";
vector<string> vec;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    string S;
    cin >> S;

    for (char c = 'a'; c <= 'm'; c++) {
        string t = alpha + c;
        sort(t.begin(), t.end());
        vec.push_back(t);
    }

    bool f = false;
    for (char c = 'a'; c <= 'm'; c++) {
        string t = S + c;
        sort(t.begin(), t.end());
        for (auto v : vec) {
            if (v == t) {
                cout << c << endl;
                f = true;
            }
        }
    }
    if (!f) {
        cout << "Impossible" << endl;
    }

    return 0;
}