#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100 + 55;
string a[MAXN];
string ans = "";
int used[MAXN];
bool cycle = 0;
vector<int> g[MAXN];
void dfs(int v) {
  used[v] = 1;
  for (auto i : g[v]) {
    if (used[i] == 1) {
      cycle = 1;
      break;
    } else if (!used[i]) {
      dfs(i);
    }
  }
  ans.push_back(v + 'a');
  used[v] = 2;
}
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  for (int i = 1; i < n; i++) {
    int cnt = 0;
    bool f = 0;
    for (int j = 0; j < min(a[i + 1].size(), a[i].size()); j++) {
      if (a[i][cnt] != a[i + 1][j]) {
        g[a[i + 1][cnt] - 'a'].push_back(a[i][j] - 'a');
        f = 1;
        break;
      }
      cnt++;
    }
    if (!f) {
      if (a[i].size() == cnt) {
        continue;
      } else {
        cout << "Impossible";
        return 0;
      }
    }
  }
  for (int i = 25; i >= 0; i--)
    if (!used[i]) dfs(i);
  if (!cycle) {
    cout << ans;
  } else {
    cout << "Impossible";
  }
}
