#include <bits/stdc++.h>
using namespace std;
vector<int> b[28];
int indeg[28];
bool ok = 1;
int main() {
  int n;
  memset((indeg), (0), sizeof(indeg));
  string a[110];
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i];
  for (int i = 0; i < n - 1; i++) {
    int j = 0;
    while (j < a[i].size() && j < a[i + 1].size() && a[i][j] == a[i + 1][j])
      j++;
    if (j == a[i + 1].length() && j < a[i].size()) {
      ok = 0;
    } else if (j < a[i].length() && j < a[i + 1].length()) {
      b[a[i][j] - 'a'].push_back(a[i + 1][j] - 'a');
      indeg[a[i + 1][j] - 'a']++;
    }
  }
  queue<int> q;
  vector<int> ans;
  for (int i = 0; i < 26; i++)
    if (indeg[i] == 0) q.push(i);
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    ans.push_back(u);
    for (int i = 0; i < b[u].size(); i++) {
      indeg[b[u][i]]--;
      if (indeg[b[u][i]] == 0) q.push(b[u][i]);
    }
  }
  if (ans.size() != 26) ok = 0;
  if (!ok)
    puts("Impossible");
  else {
    for (int i = 0; i < 26; i++) printf("%c", ans[i] + 'a');
    printf("\n");
  }
  return 0;
}
