#include <bits/stdc++.h>
using namespace std;
void Fast_IO() {
  ios::sync_with_stdio(0);
  cin.tie(0);
}
bool Impossible = false;
long long isroot[26];
vector<vector<long long> > adj(26);
long long vis[26];
string ans = "";
void compare(string s, string t) {
  if ((long long)int(s.length()) > (long long)int(t.length()) &&
      s.substr(0, (long long)int(t.length())) == t) {
    Impossible = true;
    return;
  }
  for (long long i = (long long)0;
       i <= (long long)(long long)int(s.length()) - 1; i++)
    if (s[i] != t[i]) {
      adj[s[i] - 'a'].push_back(t[i] - 'a');
      isroot[t[i] - 'a']++;
      return;
    }
}
void dfs(long long u) {
  vis[u] = 1;
  for (auto v : adj[u]) {
    if (vis[v] == 1) {
      Impossible = true;
      continue;
    } else if (vis[v] == 2)
      continue;
    dfs(v);
  }
  ans.push_back('a' + u);
  vis[u] = 2;
}
int main() {
  Fast_IO();
  long long n;
  cin >> n;
  string s[n];
  for (long long i = (long long)0; i <= (long long)n - 1; i++) cin >> s[i];
  for (long long i = (long long)0; i <= (long long)25; i++) isroot[i] = 0;
  for (long long i = (long long)0; i <= (long long)n - 2; i++)
    compare(s[i], s[i + 1]);
  if (Impossible) {
    cout << "Impossible" << '\n';
    return 0;
  }
  for (long long i = (long long)0; i <= (long long)25; i++) vis[i] = 0;
  for (long long i = (long long)0; i <= (long long)25; i++)
    if (isroot[i] == 0) dfs(i);
  reverse(ans.begin(), ans.end());
  if (Impossible || (long long)int(ans.size()) != 26)
    cout << "Impossible";
  else
    cout << ans;
  return 0;
}
