#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int N;
  cin >> N;
  vector<string> A(N);
  for (int i = 0; i < N; i++) cin >> A[i];
  vector<vector<int>> X(26, vector<int>(26, 0));
  bool fail = false;
  for (int i = 0; i < N - 1; i++) {
    string s = A[i];
    string t = A[i + 1];
    int j = 0;
    while (j != s.size() && j != t.size() && s[j] == t[j]) j++;
    if (j == s.size()) {
    } else if (j == t.size()) {
      fail = true;
    } else {
      int a = s[j] - 'a';
      int b = t[j] - 'a';
      if (X[a][b] == 1) fail = true;
      X[a][b] = -1;
      if (X[b][a] == -1) fail = true;
      X[b][a] = 1;
    }
  }
  if (fail) {
    cout << "Impossible" << endl;
    return 0;
  }
  for (int i = 0; i < 26; i++) {
    for (int j = 0; j < 26; j++) {
      cerr << X[i][j] << " ";
    }
    cerr << endl;
  }
  vector<bool> used(26, false);
  string out;
  for (int k = 0; k < 26; k++) {
    int next = -1;
    for (int i = 0; i < 26; i++) {
      if (used[i]) continue;
      bool less = true;
      for (int j = 0; j < 26; j++) {
        if (used[j]) continue;
        if (X[i][j] > 0) less = false;
      }
      if (less) {
        next = i;
        break;
      }
    }
    if (next == -1) {
      fail = true;
      break;
    }
    used[next] = true;
    out += (char)('a' + next);
  }
  if (fail) {
    cout << "Impossible" << endl;
    return 0;
  }
  cout << out << endl;
  return 0;
}
