#include <bits/stdc++.h>
using namespace std;
bitset<26> vis, use;
vector<int> topo;
vector<int> g[26];
vector<string> s;
bool dfs(int u) {
  vis[u] = true;
  use[u] = true;
  for (auto& v : g[u]) {
    if (use[v]) {
      return true;
    } else if (!vis[v] and dfs(v)) {
      return true;
    }
  }
  use[u] = false;
  topo.push_back(u);
  return false;
}
bool lex(int i) {
  int n = min(s[i].size(), s[i + 1].size());
  for (int j = 0; j < n; j++) {
    if (s[i][j] != s[i + 1][j]) {
      g[s[i][j] - 'a'].push_back(s[i + 1][j] - 'a');
      return true;
    }
  }
  return s[i].size() <= s[i + 1].size();
}
int main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  s.assign(n, string());
  for (int i = 0; i < n; i++) {
    cin >> s[i];
  }
  for (int i = 0; i + 1 < n; i++) {
    if (!lex(i)) {
      cout << "Impossible\n";
      return 0;
    }
  }
  for (int i = 0; i < 26; i++) {
    if (!vis[i] and dfs(i)) {
      printf("Impossible\n");
      return 0;
    }
  }
  reverse(topo.begin(), topo.end());
  for (int i = 0; i < 26; i++) cout << (char)(topo[i] + 'a');
  cout << '\n';
  return 0;
}
