#include <bits/stdc++.h>
using namespace std;
bool adj_matrix[26][26] = {};
bool visited[26] = {};
vector<long long> order;
long long numbering[26];
void dfs(long long node) {
  visited[node] = true;
  for (long long neigh = 0; neigh < 26; ++neigh) {
    if (!visited[neigh] && adj_matrix[node][neigh]) {
      dfs(neigh);
    }
  }
  order.push_back(node);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  long long n;
  cin >> n;
  if (n == 1) {
    for (long long i = 0; i < 26; ++i) {
      cout << char('a' + i);
    }
    return 0;
  }
  char str[2][105];
  cin >> str[1];
  for (long long i = 2; i <= n; ++i) {
    long long curr = (i & 1), prev = 1 - curr;
    cin >> str[curr];
    long long k = 0;
    for (; str[prev][k] && str[curr][k]; ++k) {
      if (str[prev][k] != str[curr][k]) {
        adj_matrix[str[prev][k] - 'a'][str[curr][k] - 'a'] = true;
        break;
      }
    }
    if (str[prev][k] && !str[curr][k]) {
      cout << "Impossible";
      return 0;
    }
  }
  for (long long i = 0; i < 26; ++i) {
    if (!visited[i]) {
      dfs(i);
    }
  }
  reverse(order.begin(), order.end());
  for (long long i = 0; i < 26; ++i) {
    for (long long j = i + 1; j <= 25; ++j) {
      if (adj_matrix[order[j]][order[i]]) {
        cout << "Impossible";
        return 0;
      }
    }
  }
  for (auto o : order) {
    cout << char(o + 'a');
  }
  return 0;
}
