#include <bits/stdc++.h>
using namespace std;
const int W = 0;
const int G = 1;
const int B = 2;
vector<vector<int> > g(50);
bool IMP;
int eqlen(string a, string b) {
  int cnt = 0;
  while (a[cnt] == b[cnt]) cnt++;
  return cnt;
}
void make_edge(string a, string b) {
  if (a.empty()) return;
  if (b.empty()) {
    IMP = 1;
    return;
  }
  int ia = a[0] - 'a';
  int ib = b[0] - 'a';
  g[ia].push_back(ib);
}
void find_circles(int v, int p, vector<int>& used) {
  used[v] = G;
  for (int i = 0; i < g[v].size(); i++) {
    int to = g[v][i];
    if (used[to] == B) continue;
    if (used[to] == G) {
      IMP = 1;
      break;
    }
    find_circles(to, v, used);
  }
  used[v] = B;
}
vector<int> ans;
void ts(int v, vector<int>& used) {
  used[v] = 1;
  for (int i = 0; i < g[v].size(); i++) {
    int to = g[v][i];
    if (used[to]) continue;
    ts(to, used);
  }
  ans.push_back(v);
}
int main() {
  int n;
  cin >> n;
  string last;
  cin >> last;
  for (int i = 1; i < n; ++i) {
    string now;
    cin >> now;
    int len = eqlen(last, now);
    make_edge(last.substr(len, 1), now.substr(len, 1));
    last = now;
  }
  vector<int> used(30, 0);
  for (int i = 0; i < 30; i++) {
    if (used[i]) continue;
    find_circles(i, -1, used);
  }
  used = vector<int>(30, 0);
  if (IMP) {
    cout << "Impossible" << endl;
    return 0;
  }
  for (int i = 0; i < 26; i++) {
    if (used[i]) continue;
    ts(i, used);
  }
  reverse(ans.begin(), ans.end());
  for (int i = 0; i < ans.size(); i++) {
    cout << char(ans[i] + 'a');
  }
  cout << endl;
  return 0;
}
