#include <bits/stdc++.h>
using namespace std;
string s[112];
vector<int> graph[30];
bool visit[30];
bool recStack[30];
stack<int> st;
bool detectCycle(int v) {
  visit[v] = true;
  recStack[v] = true;
  for (int i = 0; i < graph[v].size(); i++) {
    int nv = graph[v][i];
    if (!visit[nv]) {
      if (detectCycle(nv)) return true;
    } else {
      if (recStack[nv]) return true;
    }
  }
  recStack[v] = false;
  return false;
}
void topo(int v) {
  visit[v] = true;
  for (int i = 0; i < graph[v].size(); i++) {
    int nv = graph[v][i];
    if (!visit[nv]) {
      topo(nv);
    }
  }
  st.push(v);
}
int main() {
  int i, j, n;
  cin >> n;
  for (int i = 0; i < (n); i++) {
    cin >> s[i];
  }
  for (int i = 0; i < (n - 1); i++) {
    int l1 = s[i].length();
    int l2 = s[i + 1].length();
    for (j = 0; j < l1 && j < l2; j++) {
      if (s[i][j] == s[i + 1][j])
        continue;
      else {
        int one = s[i][j] - 'a';
        int two = s[i + 1][j] - 'a';
        graph[one].push_back(two);
        break;
      }
    }
    if (j == min(l1, l2)) {
      if (l1 > l2) {
        printf("%s\n", "Impossible");
        return 0;
      }
    }
  }
  for (int i = 0; i < 26; i++) {
    if (!visit[i]) {
      if (detectCycle(i)) {
        cout << "Impossible\n";
        return 0;
      }
    }
  }
  memset(visit, false, sizeof visit);
  for (int i = 0; i < 26; i++) {
    if (!visit[i]) {
      topo(i);
    }
  }
  string str = "";
  while (!st.empty()) {
    char ch = (char)st.top() + 'a';
    st.pop();
    str.push_back(ch);
  }
  cout << str << endl;
  return 0;
}
