#include <bits/stdc++.h>
using namespace std;
int graph[26][26];
int cnt[26], viz[26];
string s[105];
void dfs(int p) {
  viz[p] = 1;
  cout << char('a' + p);
  for (int i = 0; i < 26; i++) {
    if (graph[p][i]) cnt[i]--;
    if (cnt[i] == 0 && viz[i] == 0) dfs(i);
  }
}
int main() {
  int n, i, j, k;
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> s[i];
  for (i = 1; i <= n; i++)
    for (j = i + 1; j <= n; j++) {
      k = 0;
      while (s[i][k] == s[j][k] && k < s[i].length() && k < s[j].length()) k++;
      if (!(k >= s[i].length() || k >= s[j].length()))
        graph[s[i][k] - 'a'][s[j][k] - 'a'] = 1;
      else {
        if (k >= s[j].length()) {
          cout << "Impossible\n";
          return 0;
        }
      }
    }
  for (k = 0; k < 26; k++)
    for (i = 0; i < 26; i++)
      for (j = 0; j < 26; j++)
        if (graph[i][k] == 1 && graph[k][j] == 1) graph[i][j] = 1;
  for (i = 0; i < 26; i++)
    for (j = 0; j < 26; j++)
      if (i != j) {
        if (graph[i][j]) cnt[j]++;
        if (graph[i][j] && graph[j][i]) {
          cout << "Impossible\n";
          return 0;
        }
      }
  for (i = 0; i < 26; i++)
    if (cnt[i] == 0 && viz[i] == 0) dfs(i);
  return 0;
}
