#include <bits/stdc++.h>
using namespace std;
template <typename T>
T sgn(T x) {
  return x < 0 ? -1 : (x > 0 ? 1 : 0);
}
template <typename T>
T gcd(T a, T b) {
  return a ? gcd(b % a, a) : b;
}
template <typename T>
T abs(T x) {
  return x < 0 ? -x : x;
}
template <typename T>
T sqr(T x) {
  return x * x;
}
int n, p[26];
set<int> g[26];
void ordena() {
  int u;
  queue<int> q;
  vector<int> v;
  set<int> letras;
  for (int i = 0; i < 26; i++) letras.insert(i);
  for (int i = 0; i < 26; i++)
    if (p[i] == 0) q.push(i);
  while (!q.empty()) {
    u = q.front();
    q.pop();
    letras.erase(u);
    v.push_back(u);
    for (int x : g[u]) {
      p[x]--;
      if (p[x] == 0) q.push(x);
    }
  }
  for (int i = 0; i < 26; i++) {
    if (p[i]) {
      cout << "Impossible"
           << "\n";
      return;
    }
  }
  for (int x : letras) v.push_back(x);
  for (int x : v) cout << (char)(x + 'a');
  cout << "\n";
}
string s[123];
int pode = 1;
void solve() {
  int ta, tb, a, b;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> s[i];
  }
  for (int i = 0; i < n - 1; i++) {
    ta = (int)s[i].size();
    tb = (int)s[i + 1].size() - 1;
    for (int j = 0; j < ta; j++) {
      if (s[i][j] == s[i + 1][j]) {
        if (j == tb) {
          pode = 0;
          break;
        }
        continue;
      }
      a = s[i][j] - 'a';
      b = s[i + 1][j] - 'a';
      if (g[a].count(b) == 0) {
        g[a].insert(b);
        p[b]++;
      }
      break;
    }
    if (!pode) break;
  }
  if (pode)
    ordena();
  else
    cout << "Impossible"
         << "\n";
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
}
