#include <bits/stdc++.h>
using namespace std;
vector<string> split(const string &s, char c) {
  vector<string> v;
  stringstream ss(s);
  string x;
  while (getline(ss, x, c)) v.push_back(x);
  return v;
}
void err(vector<string>::iterator it) {}
template <typename T, typename... Args>
void err(vector<string>::iterator it, T a, Args... args) {
  cerr << it->substr((*it)[0] == ' ', it->length()) << " = " << a << '\n';
  err(++it, args...);
}
const int MOD = 1000000007;
template <class T>
inline T tmin(T a, T b) {
  return (a < b) ? a : b;
}
template <class T>
inline T tmax(T a, T b) {
  return (a > b) ? a : b;
}
template <class T>
inline void amax(T &a, T b) {
  if (b > a) a = b;
}
template <class T>
inline void amin(T &a, T b) {
  if (b < a) a = b;
}
template <class T>
inline T tabs(T a) {
  return (a > 0) ? a : -a;
}
template <class T>
T gcd(T a, T b) {
  while (b != 0) {
    T c = a;
    a = b;
    b = c % b;
  }
  return a;
}
const int N = 105;
int n;
string s[N];
vector<int> G[30], ord;
bool topologicalSort() {
  vector<int> deg(26, 0);
  for (__typeof(0) i = (0) - ((0) > (26)); i != (26) - ((0) > (26));
       i += 1 - 2 * ((0) > (26)))
    for (__typeof(0) j = (0) - ((0) > (G[i].size()));
         j != (G[i].size()) - ((0) > (G[i].size()));
         j += 1 - 2 * ((0) > (G[i].size())))
      deg[G[i][j]]++;
  ord.assign(26, -1);
  int t = 0;
  for (__typeof(0) i = (0) - ((0) > (26)); i != (26) - ((0) > (26));
       i += 1 - 2 * ((0) > (26)))
    if (deg[i] == 0) ord[t++] = i;
  for (__typeof(0) i = (0) - ((0) > (t)); i != (t) - ((0) > (t));
       i += 1 - 2 * ((0) > (t))) {
    int v = ord[i];
    for (__typeof(0) j = (0) - ((0) > (G[v].size()));
         j != (G[v].size()) - ((0) > (G[v].size()));
         j += 1 - 2 * ((0) > (G[v].size()))) {
      if (--deg[G[v][j]] == 0) ord[t++] = G[v][j];
    }
  }
  return (t == 26);
}
int main(int argc, char *argv[]) {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (__typeof(0) i = (0) - ((0) > (n)); i != (n) - ((0) > (n));
       i += 1 - 2 * ((0) > (n)))
    cin >> s[i];
  bool ok = true;
  for (__typeof(1) i = (1) - ((1) > (n)); i != (n) - ((1) > (n));
       i += 1 - 2 * ((1) > (n))) {
    int m = tmin(s[i].length(), s[i - 1].length());
    int ind = -1;
    for (__typeof(0) j = (0) - ((0) > (m)); j != (m) - ((0) > (m));
         j += 1 - 2 * ((0) > (m))) {
      if (s[i][j] != s[i - 1][j]) {
        ind = j;
        break;
      }
    }
    if (ind == -1) {
      if (s[i].length() < s[i - 1].length()) ok = false;
    } else {
      int u = s[i - 1][ind] - 'a';
      int v = s[i][ind] - 'a';
      G[u].push_back(v);
    }
  }
  if (!ok || !topologicalSort()) {
    printf("Impossible\n");
    return 0;
  }
  for (__typeof(0) i = (0) - ((0) > (26)); i != (26) - ((0) > (26));
       i += 1 - 2 * ((0) > (26)))
    printf("%c", ord[i] + 'a');
  printf("\n");
  return 0;
}
