#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void smin(T &a, U b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, U b) {
  if (a < b) a = b;
}
template <class T>
inline void gn(T &first) {
  char c, sg = 0;
  while (c = getchar(), (c > '9' || c < '0') && c != '-')
    ;
  for ((c == '-' ? sg = 1, c = getchar() : 0), first = 0; c >= '0' && c <= '9';
       c = getchar())
    first = (first << 1) + (first << 3) + c - '0';
  if (sg) first = -first;
}
template <class T, class T1>
inline void gn(T &first, T1 &second) {
  gn(first);
  gn(second);
}
template <class T, class T1, class T2>
inline void gn(T &first, T1 &second, T2 &z) {
  gn(first);
  gn(second);
  gn(z);
}
template <class T>
inline void print(T first) {
  if (first < 0) {
    putchar('-');
    return print(-first);
  }
  if (first < 10) {
    putchar('0' + first);
    return;
  }
  print(first / 10);
  putchar(first % 10 + '0');
}
template <class T>
inline void printsp(T first) {
  print(first);
  putchar(' ');
}
template <class T>
inline void println(T first) {
  print(first);
  putchar('\n');
}
template <class T, class U>
inline void print(T first, U second) {
  printsp(first);
  println(second);
}
template <class T, class U, class V>
inline void print(T first, U second, V z) {
  printsp(first);
  printsp(second);
  println(z);
}
int power(int a, int b, int m, int ans = 1) {
  for (; b; b >>= 1, a = 1LL * a * a % m)
    if (b & 1) ans = 1LL * ans * a % m;
  return ans;
}
void finish() {
  puts("Impossible");
  exit(0);
}
char s[333][333];
vector<int> adj[333];
int indeg[333], qf, qb, q[333];
int main() {
  int n;
  gn(n);
  for (int i = 0; i < n; i++) {
    scanf("%s", s[i]);
  }
  for (int i = 1; i < n; i++) {
    int la = strlen(s[i - 1]), lb = strlen(s[i]), lc = min(la, lb), j;
    for (j = 0; j < lc; j++) {
      if (s[i][j] != s[i - 1][j]) break;
    }
    if (j == lc) {
      if (la > lb) finish();
      continue;
    }
    adj[s[i - 1][j] - 'a'].push_back(s[i][j] - 'a');
    indeg[s[i][j] - 'a']++;
  }
  qf = qb = 0;
  for (int i = 0; i < 26; i++)
    if (indeg[i] == 0) q[qb++] = i;
  while (qf < qb) {
    int u = q[qf++];
    for (int j = 0; j < adj[u].size(); j++) {
      int v = adj[u][j];
      if (--indeg[v] == 0) {
        q[qb++] = v;
      }
    }
  }
  if (qb != 26) finish();
  for (int i = 0; i < qb; i++) putchar('a' + q[i]);
  return 0;
}
