#include <bits/stdc++.h>
using namespace std;
long long power(long long a, long long b) {
  long long res = 1;
  while (b > 0) {
    if (b & 1) res = res * a;
    a = a * a;
    b >>= 1;
  }
  return res;
}
long long logx(long long base, long long num) {
  int cnt = 0;
  while (num != 1) {
    num /= base;
    ++cnt;
  }
  return cnt;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return (a / gcd(a, b)) * b; }
void print(vector<long long> a) {
  for (int i = 0; i < a.size(); i++) {
    cout << a[i] << ' ';
  }
  cout << "\n";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int d[30][30];
  char c[30], t;
  int n, i, j, k;
  cin >> n;
  char s[200][200];
  for (i = 0; i < n; i++) cin >> s[i];
  for (i = 1; i < n; i++) {
    for (j = 0; s[i][j] && s[i][j] == s[i - 1][j]; j++)
      ;
    if (s[i][j] && s[i - 1][j]) d[s[i][j] - 'a'][s[i - 1][j] - 'a'] = 1;
    if (!s[i][j] && s[i - 1][j]) {
      cout << "Impossible"
           << "\n";
      return 0;
    }
  }
  for (i = 0; i < 26; i++) c[i] = i + 'a';
  for (i = 0; i < 1000; i++)
    for (j = 0; j < 26; j++)
      for (k = j + 1; k < 26; k++)
        if (d[c[j] - 'a'][c[k] - 'a']) {
          t = c[j];
          c[j] = c[k];
          c[k] = t;
        }
  for (j = 0; j < 26; j++)
    for (k = j + 1; k < 26; k++)
      if (d[c[j] - 'a'][c[k] - 'a']) {
        cout << "Impossible"
             << "\n";
        return 0;
      }
  cout << c << "\n";
  return 0;
}
