#include <bits/stdc++.h>
using namespace std;
const long long int MOD = 1e9 + 7;
const long long int INF = 998244353;
const long long int N = 1e6 + 1;
stack<int> s;
bool cyclic(vector<int> path[], bool vis[], bool recstack[], int node) {
  if (!vis[node]) {
    vis[node] = true;
    recstack[node] = true;
    for (int i = 0; i < path[node].size(); i++) {
      int j = path[node][i];
      if (!vis[j] && cyclic(path, vis, recstack, j)) {
        return true;
      } else if (recstack[j]) {
        return true;
      }
    }
  }
  recstack[node] = false;
  return false;
}
void dfs(int node, vector<int> path[], bool vis[]) {
  if (vis[node]) {
    return;
  }
  vis[node] = true;
  for (int i = 0; i < path[node].size(); i++) {
    int j = path[node][i];
    if (!vis[j]) {
      dfs(j, path, vis);
    }
  }
  s.push(node);
}
void solve() {
  long long int n;
  cin >> n;
  bool vis[26] = {0};
  string prev, curr;
  cin >> prev;
  vector<int> path[26];
  for (int i = 1; i < n; i++) {
    cin >> curr;
    int mini = min(prev.length(), curr.length());
    bool flag = false;
    for (int j = 0; j < mini; j++) {
      if (prev[j] != curr[j]) {
        flag = true;
        path[prev[j] - 'a'].push_back(curr[j] - 'a');
        break;
      }
    }
    if (flag == false && prev.length() > curr.length()) {
      cout << "Impossible" << '\n';
      return;
    }
    prev = curr;
  }
  bool recstack[26] = {0};
  for (int i = 0; i < 26; i++) {
    if (cyclic(path, vis, recstack, i)) {
      cout << "Impossible" << '\n';
      return;
    }
  }
  memset(vis, 0, sizeof(vis));
  for (int i = 25; i >= 0; i--) {
    if (!vis[i]) {
      dfs(i, path, vis);
    }
  }
  while (!s.empty()) {
    char c = s.top() + 'a';
    s.pop();
    cout << c;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin.tie(0);
  cout.tie(0);
  long long int t;
  long long int m = 0;
  t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
