#include <bits/stdc++.h>
using namespace std;
struct node {
  int data, num;
};
char s[110][110], ans[110];
int g[100][100], l[110];
node a[110];
bool operator<(node a, node b) { return (a.data < b.data); }
void push(int x, int y) { g[x][y] = 1; }
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%s", s[i]);
    l[i] = strlen(s[i]);
  }
  memset(g, 0, sizeof(g));
  for (int i = 1; i <= 26; i++) g[i][i] = 1;
  for (int i = 1; i < n; i++)
    for (int j = i + 1; j <= n; j++) {
      bool ok = 1;
      for (int k = 0; k < min(l[i], l[j]); k++)
        if (s[i][k] != s[j][k]) {
          push(int(s[i][k]) - 96, int(s[j][k]) - 96);
          ok = 0;
          break;
        }
      if (ok && l[i] > l[j]) {
        printf("Impossible\n");
        return 0;
      }
    }
  for (int i = 1; i <= 26; i++)
    for (int j = 1; j <= 26; j++)
      for (int k = 1; k <= 26; k++) g[j][k] = g[j][k] | (g[j][i] & g[i][k]);
  for (int i = 1; i < 26; i++)
    for (int j = i + 1; j <= 26; j++)
      if (g[i][j] && g[j][i]) {
        printf("Impossible\n");
        return 0;
      }
  for (int i = 1; i <= 26; i++) {
    a[i].num = i;
    a[i].data = 0;
    for (int j = 1; j <= 26; j++)
      if (g[j][i]) a[i].data++;
  }
  sort(a + 1, a + 27);
  for (int i = 1; i <= 26; i++) putchar(a[i].num + 96);
  putchar('\n');
  return 0;
}
