#include <bits/stdc++.h>
using namespace std;
const int N = 110;
const int z = 26;
int edge[z][z];
int clr[z], mrk[z];
string s[N];
bool impossible = false;
stack<int> st;
void dfs(int cur) {
  clr[cur] = 1;
  for (int i = 0; i < z; i++) {
    if (edge[cur][i]) {
      if (clr[i] == 0) {
        dfs(i);
      } else if (clr[i] == 1) {
        impossible = true;
        return;
      }
    }
  }
  clr[cur] = 2;
}
void dfs1(int cur) {
  mrk[cur] = 1;
  for (int i = 0; i < z; i++) {
    if (edge[cur][i]) {
      if (!mrk[i]) {
        dfs1(i);
      }
    }
  }
  st.push(cur);
}
int main() {
  ios_base ::sync_with_stdio(false);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> s[i];
  }
  for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
      int ii = 0, jj = 0;
      while (s[i][ii] && s[j][jj] && s[i][ii] == s[j][jj]) ii++, jj++;
      if (s[i][ii] && s[j][jj]) {
        edge[s[i][ii] - 'a'][s[j][jj] - 'a'] = 1;
      } else {
        if (s[i][ii]) {
          impossible = true;
          break;
        }
      }
    }
    if (impossible) break;
  }
  if (impossible) {
    puts("Impossible");
    return 0;
  }
  for (int i = 0; i < z; i++) {
    if (clr[i] == 0) {
      dfs(i);
    }
  }
  if (impossible) {
    puts("Impossible");
  } else {
    for (int i = 0; i < z; i++) {
      if (!mrk[i]) {
        dfs1(i);
      }
    }
    while (!st.empty()) {
      char ch = (char)(st.top() + 'a');
      cout << ch;
      st.pop();
    }
    cout << endl;
  }
}
