#include <bits/stdc++.h>
using namespace std;
int n;
vector<string> vi;
string s;
int indeg[26];
set<int> st;
vector<int> g[26];
string ans;
void toposort(vector<int> g[], int &count) {
  while (st.size() != 0) {
    count += 1;
    int top = *st.begin();
    ans += (char)(top);
    st.erase(st.begin());
    for (int v : g[top - 97]) {
      indeg[v]--;
      if (indeg[v] == 0) st.insert(v + 97);
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> s;
    vi.push_back(s);
  }
  int poss = 0;
  for (int i = 0; i < n - 1; i++) {
    string s = vi[i];
    string s1 = vi[i + 1];
    for (int j = 0; j < min(s.size(), s1.size()); j++) {
      if (s[j] != s1[j]) {
        g[s[j] - 'a'].push_back(s1[j] - 'a');
        indeg[s1[j] - 'a']++;
        break;
      }
      if (j == s1.size() - 1 && (s.size() > s1.size())) poss = 1;
    }
  }
  int count = 0;
  for (int i = 0; i < 26; i++) {
    if (indeg[i] == 0) st.insert(97 + i);
  }
  toposort(g, count);
  if (count != 26 || poss)
    cout << "Impossible"
         << "\n";
  else
    cout << ans << "\n";
}
