#include <bits/stdc++.h>
using namespace std;
string s[103];
char alph[103];
int was[103];
set<char> bigger[103];
int cnt;
void go() {
  for (int i = 0; i < 26; i++) {
    if (was[i] == 0) {
      if (bigger[i].empty()) {
        alph[cnt++] = (char)(i + 'a');
        was[i] = 1;
        for (int j = 0; j < 26; j++) {
          if (was[j] == 0) {
            if (bigger[j].find((char)(i + 'a')) != bigger[j].end())
              bigger[j].erase((char)(i + 'a'));
          }
        }
      }
    }
  }
}
int main() {
  int n;
  bool ok = true;
  cnt = 0;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> s[i];
  }
  for (int i = 1; i < n; i++) {
    if (!ok) break;
    for (int j = 0; j < s[i - 1].length(); j++) {
      if (j >= s[i].length()) {
        ok = false;
        break;
      }
      if (s[i][j] == s[i - 1][j]) continue;
      bigger[(int)(s[i][j] - 'a')].insert(s[i - 1][j]);
      break;
    }
  }
  if (!ok) {
    cout << "Impossible";
    return 0;
  }
  for (int i = 0; i < 26; i++) go();
  if (alph[25] == alph[50])
    cout << "Impossible";
  else {
    for (int i = 0; i < 26; i++) cout << alph[i];
  }
  return 0;
}
