#include <bits/stdc++.h>
using namespace std;
map<int, vector<int> > mapp;
map<int, int> vis;
string ans;
bool topo() {
  vector<int> in(26, 0);
  int i, j;
  for (i = 0; i < 26; i++) {
    for (auto child : mapp[i]) {
      in[child]++;
    }
  }
  queue<int> q;
  for (i = 0; i < 26; i++) {
    if (in[i] == 0) {
      q.push(i);
    }
  }
  int count = 0, temp;
  while (!q.empty()) {
    temp = q.front();
    q.pop();
    ans.push_back(temp + 'a');
    for (auto child : mapp[temp]) {
      in[child]--;
      if (in[child] == 0) {
        q.push(child);
      }
    }
    count++;
  }
  if (count != 26) {
    return false;
  }
  return true;
}
void solve() {
  int i, j;
  int n;
  cin >> n;
  string s[n];
  char ch;
  for (i = 0; i < n; i++) {
    cin >> s[i];
  }
  int sz, root = -1;
  for (i = 0; i <= n - 2; i++) {
    sz = min(s[i].size(), s[i + 1].size());
    for (j = 0; j < sz; j++) {
      if (s[i][j] != s[i + 1][j]) {
        mapp[s[i][j] - 'a'].push_back(s[i + 1][j] - 'a');
        vis[s[i][j] - 'a']++;
        vis[s[i + 1][j] - 'a']++;
        if (root == -1) {
          root = s[i][j] - 'a';
        }
        break;
      }
      if (j == sz - 1) {
        if (s[i].size() > sz) {
          cout << "Impossible\n";
          return;
        }
      }
    }
  }
  if (root == -1) {
    for (j = 0; j < 26; j++) {
      cout << char('a' + j);
    }
    return;
  }
  if (topo() == false) {
    cout << "Impossible\n";
  } else {
    for (i = 0; i < 26; i++) {
      ch = 'a' + i;
      for (j = 0; j < ans.size(); j++) {
        if (ans[j] == ch) {
          break;
        } else if (j == ans.size() - 1) {
          ans.push_back(ch);
        }
      }
    }
    cout << ans << '\n';
  }
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
