#include <bits/stdc++.h>
using namespace std;
const int NMAX = 110, ALPHA = 26;
int N, TopSort[NMAX], Len[NMAX], PosTS[ALPHA];
char S[NMAX][NMAX];
vector<int> G[ALPHA];
bool Used[NMAX], HaveCycle;
void BuildGraph(int Left, int Right, int Pos) {
  if (Left == Right) return;
  bool Have = 0;
  for (int i = Left; i <= Right; ++i)
    if (Len[i] < Pos) Have = 1;
  if (Have) {
    for (int i = Left; i <= Right; ++i) {
      if (Len[i] < Pos) continue;
      int L = i, R = i;
      while (R <= Right && Len[R] >= Pos) R++;
      R--;
      BuildGraph(L, R, Pos);
      i = R;
    }
    return;
  }
  for (int i = Left; i < Right; ++i)
    if (S[i][Pos] != S[i + 1][Pos]) {
      int A = S[i][Pos] - 'a', B = S[i + 1][Pos] - 'a';
      G[A].push_back(B);
    }
  for (int i = Left; i <= Right; ++i) {
    int L = i, R = i;
    while (R <= Right && S[L][Pos] == S[R][Pos]) R++;
    R--;
    BuildGraph(L, R, Pos + 1);
    i = R;
  }
}
void DFS(int Node) {
  Used[Node] = 1;
  for (int i = 0; i < G[Node].size(); ++i)
    if (!Used[G[Node][i]]) DFS(G[Node][i]);
  TopSort[++TopSort[0]] = Node;
}
bool Less(int X, int Y) {
  int i;
  for (i = 1; i <= Len[X] && i <= Len[Y]; ++i)
    if (S[X][i] != S[Y][i]) {
      int A = S[X][i] - 'a', B = S[Y][i] - 'a';
      if (PosTS[A] > PosTS[B]) return 0;
      return 1;
    }
  if (Len[X] > Len[Y]) return 0;
  return 1;
}
int main() {
  scanf("%i\n", &N);
  for (int i = 1; i <= N; ++i) gets(S[i] + 1), Len[i] = strlen(S[i] + 1);
  BuildGraph(1, N, 1);
  for (int i = 0; i < ALPHA; ++i)
    if (!Used[i]) DFS(i);
  reverse(TopSort + 1, TopSort + ALPHA + 1);
  for (int i = 1; i <= ALPHA; ++i) PosTS[TopSort[i]] = i;
  for (int i = 0; i < ALPHA; ++i)
    for (int j = 0; j < G[i].size(); ++j)
      if (PosTS[i] > PosTS[G[i][j]]) {
        printf("Impossible\n");
        return 0;
      }
  for (int i = 1; i < N; ++i)
    if (!Less(i, i + 1)) {
      printf("Impossible\n");
      return 0;
    }
  for (int i = 1; i <= ALPHA; ++i) printf("%c", TopSort[i] + 'a');
  return 0;
}
