#include <bits/stdc++.h>
using namespace std;
const int MAX = 1e2 + 7;
vector<int> adj[30];
bool hasCycle = false;
bool rel[30][30];
bool vis[30], act[30];
int dist[30];
int n;
string s[MAX];
string res = "";
void dfs(int u);
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> s[i];
  }
  for (int i = 1; i <= n - 1; ++i) {
    string s1 = s[i];
    string s2 = s[i + 1];
    int l = min(s1.size(), s2.size());
    if (s1.size() > s2.size()) {
      bool equal = true;
      for (int j = 0; j < (int)s2.size(); ++j) {
        if (s1[j] != s2[j]) {
          equal = false;
        }
      }
      if (equal) {
        cout << "Impossible\n";
        return 0;
      }
    }
    for (int j = 0; j < l; ++j) {
      if (s1[j] != s2[j]) {
        char c1 = s1[j];
        char c2 = s2[j];
        if (!rel[c2 - 'a' + 1][c1 - 'a' + 1]) {
          adj[c2 - 'a' + 1].push_back(c1 - 'a' + 1);
          rel[c2 - 'a' + 1][c1 - 'a' + 1] = true;
        }
        break;
      }
    }
  }
  for (int i = 1; i <= 26; ++i) {
    if (!vis[i]) {
      dfs(i);
    }
  }
  cout << res << "\n";
  return 0;
}
void dfs(int u) {
  vis[u] = 1;
  act[u] = 1;
  for (int v : adj[u]) {
    if (act[v]) {
      cout << "Impossible\n";
      exit(0);
    }
    if (!vis[v]) {
      dfs(v);
    }
  }
  act[u] = 0;
  res += 'a' + u - 1;
}
