#include <bits/stdc++.h>
using namespace std;
int N;
bool visited[200];
int pointer[30];
vector<string> all;
vector<vector<int> > adj;
vector<int> res;
bool generate_constraints() {
  for (int i = 1; i < all.size(); i++) {
    int l = min(all[i].size(), all[i - 1].size());
    bool flag = false;
    for (int j = 0; j < l; j++) {
      if (all[i - 1][j] != all[i][j]) {
        int u = all[i - 1][j] - 'a';
        int v = all[i][j] - 'a';
        adj[u].push_back(v);
        pointer[v]++;
        flag = true;
        break;
      }
    }
    if (!flag) {
      if (all[i - 1].size() > all[i].size()) {
        return false;
      }
    }
  }
  return true;
}
void transverse(int u) {
  res.push_back(u);
  for (int i = 0; i < adj[u].size(); i++) {
    int v = adj[u][i];
    pointer[v] -= 1;
    if (pointer[v] == 0) {
      transverse(v);
    }
  }
}
int main() {
  adj.resize(30, vector<int>());
  ios::sync_with_stdio(false);
  memset(visited, false, sizeof(visited));
  cin >> N;
  for (int i = 0; i < N; i++) {
    string tmp;
    cin >> tmp;
    all.push_back(tmp);
  }
  bool tmp = generate_constraints();
  if (!tmp) {
    cout << "Impossible" << endl;
    return 0;
  }
  queue<int> q;
  for (int i = 0; i < 26; i++) {
    if (pointer[i] == 0) {
      q.push(i);
    }
  }
  while (q.size()) {
    int u = q.front();
    q.pop();
    transverse(u);
  }
  for (int i = 0; i < 26; i++) {
    if (pointer[i] != 0) {
      cout << "Impossible" << endl;
      return 0;
    }
  }
  string ans = "";
  for (int i = 0; i < res.size(); i++) {
    ans += res[i] + 'a';
  }
  cout << ans << endl;
}
