#include <bits/stdc++.h>
using namespace std;
int a[26][26] = {0}, color[100] = {0};
string s[100];
int n, i, flag = 0, j;
struct node {
  char c;
  struct node *next;
};
node *q;
void dfs(int i) {
  node *p;
  p = (node *)malloc(sizeof(node));
  p->c = 'a' + i;
  int j;
  color[i] = 1;
  for (j = 0; j < 26; j++) {
    if (a[i][j] == 1) {
      if (color[j] == 0)
        dfs(j);
      else if (color[j] == 1)
        flag = 1;
    }
  }
  color[i] = 2;
  p->next = q;
  q = p;
  return;
}
int main() {
  node *p;
  q = NULL;
  cin >> n;
  for (i = 0; i < n; i++) cin >> s[i];
  for (i = 0; i < n - 1; i++) {
    j = 0;
    while (1) {
      if (j >= s[i + 1].length()) {
        flag = 1;
        break;
      }
      if (j >= s[i].length()) break;
      if (s[i][j] != s[i + 1][j]) {
        a[s[i][j] - 'a'][s[i + 1][j] - 'a'] = 1;
        break;
      }
      j++;
    }
  }
  for (i = 0; i < 26; i++) {
    if (color[i] == 0) dfs(i);
  }
  if (flag)
    cout << "Impossible";
  else {
    for (p = q; p != NULL; p = p->next) cout << p->c;
  }
}
