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

int main() {
  vector<int> V(13);
  string S;
  cin >> S;
  for (int i = 0; i < S.size(); i++)
    V.at(S.at(i) - 'a')++;
  int cnt = 0, ans;
  for (int i = 0; i < 13; i++) if (!V.at(i)) cnt++, ans = i;
  if (!cnt) {
    for (char c = 'a'; c <= 'm'; c++) cout << c << "\n";
  } else if (cnt == 1) {
    cout << char('a' + ans) << "\n";
  } else {
    cout << "Impossible" << "\n";
  }
}