#include <bits/stdc++.h>
using namespace std;
int in[26] = {};
set<char> s[26];
vector<char> ans;
int cycle = 0;
void tsort() {
  int co = 26;
  queue<char> q;
  for (int i = 0; i < 26; i++) {
    if (in[i] == 0) {
      q.push('a' + i);
    }
  }
  while (!q.empty()) {
    char c = q.front();
    q.pop();
    ans.push_back(c);
    --co;
    set<char>::iterator it = s[c - 'a'].begin();
    for (; it != s[c - 'a'].end(); it++) {
      --in[*(it) - 'a'];
      if (in[*(it) - 'a'] == 0) {
        q.push(*(it));
      }
    }
  }
  if (co) cycle = 1;
}
int main() {
  int n;
  cin >> n;
  vector<string> v(n);
  for (int i = 0; i < n; i++) {
    cin >> v[i];
  }
  int len = 0;
  int d = 0;
  for (int i = 0; i < n - 1; i++) {
    int k = 0, l = 0;
    int lena = v[i].length();
    int lenb = v[i + 1].length();
    int f = 0;
    while (k < lena && l < lenb && v[i][k] == v[i + 1][l]) {
      ++l;
      ++k;
    }
    if (k < lena && l < lenb) {
      f = 1;
      if (s[v[i][k] - 'a'].find(v[i + 1][l]) == s[v[i][k] - 'a'].end()) {
        s[v[i][k] - 'a'].insert(v[i + 1][l]);
        ++in[v[i + 1][l] - 'a'];
      }
    } else if (lena > lenb) {
      d = 1;
      break;
    }
  }
  tsort();
  if (cycle || d) {
    cout << "Impossible\n";
    return 0;
  }
  for (int i = 0; i < 26; i++) {
    cout << ans[i];
  }
  cout << '\n';
  return 0;
}
