#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n;
  cin >> n;
  string s;
  vector<string> v;
  for (int i = 0; i < n; i++) {
    cin >> s;
    v.push_back(s);
  }
  int adj[26][26];
  int flag = 0;
  memset(adj, false, sizeof(adj));
  for (int i = 0; i < n - 1; i++) {
    string a = v[i];
    string b = v[i + 1];
    int ind = 0;
    for (int j = 0; j < min(a.length(), b.length()); j++) {
      if (a[j] != b[j]) {
        ind = 1;
        adj[a[j] - 'a'][b[j] - 'a'] = true;
        break;
      }
    }
    if (ind == 0) {
      if (a.length() > b.length()) {
        flag = 1;
        break;
      }
    }
  }
  if (flag == 1)
    cout << "Impossible" << endl;
  else {
    vector<bool> visit(26, false);
    vector<int> inord(26, 0);
    for (int i = 0; i < 26; i++) {
      for (int j = 0; j < 26; j++) {
        if (adj[i][j] == true) inord[j]++;
      }
    }
    vector<int> ans;
    priority_queue<int, vector<int>, greater<int>> pq;
    for (int i = 0; i < 26; i++) {
      if (inord[i] == 0) {
        visit[i] = true;
        pq.push(i);
      }
    }
    while (!pq.empty()) {
      int tmp = pq.top();
      pq.pop();
      ans.push_back(tmp);
      for (int j = 0; j < 26; j++) {
        if (adj[tmp][j] == true && visit[j] == false) {
          inord[j]--;
          if (inord[j] == 0) {
            pq.push(j);
            visit[j] = true;
          }
        }
      }
    }
    int ind = 0;
    for (int i = 0; i < 26; i++) {
      if (visit[i] == false) {
        ind = 1;
        break;
      }
    }
    if (ind == 1)
      cout << "Impossible" << endl;
    else {
      string fins = "";
      for (int i = 0; i < ans.size(); i++) fins += ans[i] + 'a';
      cout << fins << endl;
    }
  }
  return 0;
}
