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

int main() {
    string s;
    cin >> s;
    map<char, int> d;
    for (char c : s) d[c]++;
    string t;
    for (auto x : d) {
        t.push_back(x.first);
    }
    if (t.size() == 13) {
        for (char c = 'a'; c <= 'm'; c++) cout << c << endl;
    } else if (t.size() < 12) {
        puts("Impossible");
    } else {
        for (char c = 'a'; c <= 'm'; c++) {
            if (d[c] == 0) {
                cout << c << endl;
            }
        }
    }
}