#include <bits/stdc++.h>
using namespace std;
int n;
string a[107];
int g[107][107];
int br[107];
string ret;
void input();
void solve();
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  input();
  solve();
  return 0;
}
void input() {
  cin >> n;
  int i;
  for (i = 0; i < n; i++) {
    cin >> a[i];
  }
}
void solve() {
  int i, j, t;
  int sz;
  for (i = 0; i < n; i++) {
    for (j = i - 1; j >= 0; j--) {
      sz = min(a[i].size(), a[j].size());
      for (t = 0; t < sz; t++) {
        if (a[i][t] != a[j][t]) {
          break;
        }
      }
      if (t == sz && a[i].size() < a[j].size()) {
        cout << "Impossible\n";
        return;
      }
      if (t == sz) {
        continue;
      }
      g[a[j][t] - 'a'][a[i][t] - 'a'] = 1;
    }
  }
  for (i = 0; i < 26; i++) {
    for (j = i + 1; j < 26; j++) {
      if (g[i][j] == 1 && g[j][i] == 1) {
        break;
      }
    }
    if (j != 26) {
      cout << "Impossible\n";
      return;
    }
    if (g[i][i] == 1) {
      cout << "Impossible\n";
      return;
    }
  }
  for (i = 0; i < 26; i++) {
    br[i] = 0;
    for (j = 0; j < 26; j++) {
      br[i] += g[j][i];
    }
  }
  ret.clear();
  int h = 0;
  while (1) {
    h++;
    for (i = 0; i < 26; i++) {
      if (br[i] == 0) {
        break;
      }
    }
    if (h >= 30) {
      cout << "Impossible\n";
      return;
    }
    if (i == 26) {
      break;
    }
    ret += (i + 'a');
    br[i] = -27;
    for (j = 0; j < 26; j++) {
      if (g[i][j] == 1) {
        br[j]--;
      }
    }
  }
  if (ret.size() != 26) {
    cout << "Impossible\n";
    return;
  }
  cout << ret << "\n";
}
