#include <bits/stdc++.h>
using namespace std;
map<char, vector<char>> g;
map<char, int> c;
map<char, bool> used;
vector<char> ans;
char f;
pair<char, char> makeRule(string less, string more) {
  int len = min((int)less.length(), (int)more.length());
  for (int i = 0; i < len; i++) {
    if (less[i] != more[i]) {
      return {less[i], more[i]};
    }
  }
  return {'Z', 'Z'};
}
bool isCycled(char v) {
  c[v] = 1;
  for (int i = 0; i < g[v].size(); i++) {
    int to = g[v][i];
    if (c[to] == 0) {
      if (isCycled(to)) return true;
    } else if (c[to] == 1) {
      return true;
    }
  }
  c[v] = 2;
  return false;
}
void dfs(char v) {
  used[v] = true;
  for (int i = 0; i < g[v].size(); i++) {
    char to = g[v][i];
    if (!used[to]) {
      dfs(to);
    }
  }
  ans.push_back(v);
}
void topSort() {
  for (char i = 'a'; i <= 'z'; i++) {
    if (g[i].size() > 0)
      if (!used[i]) dfs(i);
  }
  reverse(ans.begin(), ans.end());
}
int main() {
  bool flag = true;
  int n;
  cin >> n;
  for (char i = 'a'; i <= 'z'; i++) {
    c[i] = 0;
    g[i] = vector<char>();
    used[i] = false;
  }
  vector<string> words;
  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;
    words.push_back(s);
  }
  for (int i = 0; i < n; i++) {
    for (int j = i; j < n; j++) {
      if (j != i) {
        auto rule = makeRule(words[i], words[j]);
        if (rule.first == 'Z' && words[j].length() < words[i].length()) {
          flag = false;
          break;
        }
        g[rule.first].push_back(rule.second);
      }
    }
    if (!flag) break;
  }
  for (char i = 'a'; i <= 'z'; i++) {
    if (isCycled(i)) {
      flag = false;
      break;
    }
  }
  if (flag) {
    topSort();
    for (char i = 'a'; i <= 'z'; i++) {
      if (!used[i]) ans.push_back(i);
    }
    for (int i = 0; i < 26; i++) {
      cout << ans[i];
    }
  } else {
    cout << "Impossible";
  }
  return 0;
}
