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

int main() {
    bool has[256] {};
    string s;
    cin >> s;
    for (char c : s) has[c] = true;
    char missing;
    int cnt = 0;
    for (char c = 'a'; c <= 'm'; c++)
        if (!has[c]) {
            missing = c;
            cnt++;
        }
    if (cnt == 0) for (char c = 'a'; c <= 'm'; c++) cout << c << endl;
    else if (cnt == 1) cout << missing << endl;
    else cout << "Impossible\n";
    return 0;
}