#include <bits/stdc++.h>
using namespace std;
class TopologicalSort {
  using Graph = std::vector<std::vector<int>>;
  int V;
  std::vector<std::vector<int>> G;
  void dfs(int v, std::vector<int> &res, std::vector<int> &used) {
    used[v] = 1;
    for (auto to : G[v])
      if (used[to] == 0) {
        dfs(to, res, used);
      }
    res.push_back(v);
  }

 public:
  TopologicalSort(int _v) : V(_v), G(_v) {}
  void addEdge(int a, int b) {
    assert(0 <= a && a < V);
    assert(0 <= b && b < V);
    G[a].push_back(b);
  }
  std::vector<int> topologicalSort() {
    std::vector<int> ide(V);
    for (int i = 0; i < V; i++) {
      for (auto to : G[i]) {
        ide[to]++;
      }
    }
    std::vector<int> res;
    std::vector<int> used(V);
    for (int i = V - 1; i >= 0; i--) {
      if (ide[i] == 0) {
        dfs(i, res, used);
      }
    }
    if (res.size() == 0) res = {-1};
    reverse(res.begin(), res.end());
    return res;
  }
};
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<string> s(n);
  for (int i = 0; i < n; i++) cin >> s[i];
  TopologicalSort g(26);
  for (int i = 0; i < n - 1; i++) {
    int l1 = s[i].size(), l2 = s[i + 1].size();
    if (l1 > l2) {
      if (s[i].substr(0, l2) == s[i + 1].substr(0, l2)) {
        cout << "Impossible" << endl;
        return 0;
      }
    }
    for (int j = 0; j < min(l1, l2); j++) {
      if (s[i][j] == s[i + 1][j]) continue;
      g.addEdge(s[i][j] - 'a', s[i + 1][j] - 'a');
      break;
    }
  }
  auto ret = g.topologicalSort();
  vector<int> pos(26);
  if (ret.size() != 26) {
    cout << "Impossible" << endl;
    return 0;
  }
  for (int i = 0; i < 26; i++) {
    pos[ret[i]] = i;
  }
  for (int i = 0; i < n - 1; i++) {
    int l1 = s[i].size(), l2 = s[i + 1].size();
    for (int j = 0; j < min(l1, l2); j++) {
      if (s[i][j] == s[i + 1][j]) continue;
      int st = s[i][j] - 'a', gt = s[i + 1][j] - 'a';
      if (pos[st] >= pos[gt]) {
        cout << "Impossible" << endl;
        return 0;
      }
      break;
    }
  }
  for (int i = 0; i < 26; i++) {
    cout << char('a' + ret[i]);
  }
  cout << endl;
}
