#include <bits/stdc++.h>
using namespace std;
void getre() {
  int x = 0;
  printf("%d\n", 1 / x);
}
void gettle() {
  int res = 1;
  while (1) res <<= 1;
  printf("%d\n", res);
}
template <typename T, typename S>
inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S>
inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
template <typename N, typename PN>
inline N flo(N a, PN b) {
  return a >= 0 ? a / b : -((-a - 1) / b) - 1;
}
template <typename N, typename PN>
inline N cei(N a, PN b) {
  return a > 0 ? (a - 1) / b + 1 : -(-a / b);
}
template <typename N>
N gcd(N a, N b) {
  return b ? gcd(b, a % b) : a;
}
template <typename N>
inline int sgn(N a) {
  return a > 0 ? 1 : (a < 0 ? -1 : 0);
}
inline void gn(long long &x) {
  int sg = 1;
  char c;
  while (((c = getchar()) < '0' || c > '9') && c != '-')
    ;
  c == '-' ? (sg = -1, x = 0) : (x = c - '0');
  while ((c = getchar()) >= '0' && c <= '9') x = x * 10 + c - '0';
  x *= sg;
}
inline void gn(int &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(unsigned long long &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gn(long double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gs(char *s) { scanf("%s", s); }
inline void gc(char &c) {
  while ((c = getchar()) > 126 || c < 33)
    ;
}
inline void pc(char c) { putchar(c); }
inline long long sqr(long long a) { return a * a; }
inline double sqrf(double a) { return a * a; }
const int inf = 0x3f3f3f3f;
const double pi = 3.14159265358979323846264338327950288L;
const double eps = 1e-6;
const int mo = 1;
int qp(int a, long long b) {
  int n = 1;
  do {
    if (b & 1) n = 1ll * n * a % mo;
    a = 1ll * a * a % mo;
  } while (b >>= 1);
  return n;
}
string a[111];
int go[26][26];
int n;
int deg[26];
int off[26];
char ans[33];
int tot = 0;
int main() {
  gn(n);
  for (int i = (0), _ed = (n); i < _ed; i++) cin >> a[i];
  for (int i = (0), _ed = (n - 1); i < _ed; i++) {
    if (a[i] == a[i + 1]) continue;
    int j = 0;
    while (j < ((int)(a[i]).size()) && j < ((int)(a[i + 1]).size()) &&
           a[i][j] == a[i + 1][j])
      j++;
    if (j == ((int)(a[i + 1]).size())) {
      go[0][1] = go[1][0] = 1;
      break;
    }
    if (j == ((int)(a[i]).size())) continue;
    go[a[i][j] - 'a'][a[i + 1][j] - 'a'] = 1;
  }
  for (int i = (0), _ed = (26); i < _ed; i++)
    for (int j = (0), _ed = (26); j < _ed; j++)
      if (go[i][j]) deg[j]++;
  while (1) {
    int bo = 0;
    for (int i = (0), _ed = (26); i < _ed; i++)
      if (!off[i] && deg[i] == 0) {
        bo = 1;
        ans[tot++] = i + 'a';
        off[i] = 1;
        for (int j = (0), _ed = (26); j < _ed; j++)
          if (go[i][j]) {
            deg[j]--;
          }
        break;
      }
    if (!bo) break;
  }
  if (tot < 26)
    printf("Impossible\n");
  else
    printf("%s", ans);
  return 0;
}
