#include <bits/stdc++.h>
using namespace std;
const long long N = 1e5 + 7;
const long long inf = 1e9 + 7;
const long long mod = 1e9 + 7;
int n;
string s;
string t;
string res;
int k = 1000;
int used[27];
vector<int> g[27];
int f(char x) { return (x - 'a'); }
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> s;
  for (int i = 1; i < n; i++) {
    cin >> t;
    int j = 0, mx_j = min((int)t.size(), (int)s.size());
    while (j < mx_j && s[j] == t[j]) {
      j++;
    }
    if (j == (int)s.size()) {
      continue;
    }
    if (j == (int)t.size()) {
      cout << "Impossible\n";
      return 0;
    }
    used[f(t[j])]++;
    g[f(s[j])].push_back(f(t[j]));
    s = t;
  }
  int i = 0;
  while (k--) {
    if (used[i] == 0) {
      used[i]--;
      res += char(i + 'a');
      for (auto x : g[i]) {
        used[x]--;
      }
    }
    i = (i + 1) % 26;
  }
  if ((int)res.size() != 26) {
    cout << "Impossible\n";
    return 0;
  }
  cout << res << "\n";
}
