#include <bits/stdc++.h>
using namespace std;
int n;
const int N = 105;
char s[N][N];
vector<char> fr[26];
bool visited[26];
bool Forward[26];
int level[26];
bool comp(pair<int, char> a, pair<int, char> b) {
  if (a.first != b.first)
    return a.first < b.first;
  else
    return a.second > b.second;
}
bool DFS(char c) {
  if (visited[c - 'a'] && Forward[c - 'a'])
    return true;
  else if (visited[c - 'a'])
    return false;
  bool ret = false;
  visited[c - 'a'] = true;
  Forward[c - 'a'] = true;
  for (int i = 0; i < fr[c - 'a'].size(); i++) {
    level[fr[c - 'a'][i] - 'a'] =
        max(level[fr[c - 'a'][i] - 'a'], level[c - 'a'] + 1);
    ret = (ret || DFS(fr[c - 'a'][i]));
  }
  Forward[c - 'a'] = false;
  return ret;
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%s", s[i]);
  for (int i = 1; i < n; i++) {
    int j;
    int len1 = (int)strlen(s[i]);
    int len2 = (int)strlen(s[i - 1]);
    for (j = 0; j < min(len1, len2); j++) {
      if (s[i][j] != s[i - 1][j]) {
        fr[s[i - 1][j] - 'a'].push_back(s[i][j]);
        level[s[i][j] - 'a'] =
            max(level[s[i][j] - 'a'], level[s[i - 1][j] - 'a'] + 1);
        break;
      }
      if (j == min(len1, len2) - 1) {
        if (len2 > len1) {
          printf("Impossible");
          return 0;
        }
      }
    }
  }
  for (int i = 0; i < 26; i++) {
    if (!visited[i] && DFS(char(i + 'a'))) {
      printf("Impossible");
      return 0;
    }
  }
  vector<pair<int, char> > ans;
  for (int i = 0; i < 26; i++)
    ans.emplace_back(pair<int, char>(level[i], char(i + 'a')));
  sort(ans.begin(), ans.end(), comp);
  for (int i = 0; i < ans.size(); i++) printf("%c", ans[i].second);
  return 0;
}
