#include <bits/stdc++.h>
using namespace std;
vector<int> g[26];
int visit[26], recur[26];
stack<int> st;
int n, flag;
int topo(int n) {
  visit[n] = 1;
  recur[n] = 1;
  for (auto a : g[n]) {
    if (recur[a]) {
      flag = 0;
      return -1;
    }
    if (!visit[a]) {
      if (topo(a) == -1) return -1;
    }
  }
  recur[n] = 0;
  st.push(n);
  return 0;
}
string printOrder() {
  flag = 1;
  int j, k, mx = -1;
  memset(visit, 0, 26 * 4);
  for (int i = 0; i < 26; i++) g[i].clear();
  string dict[n];
  for (int i = 0; i < n; i++) {
    cin >> dict[i];
  }
  for (int i = 0; i < n - 1; i++) {
    for (j = 0, k = 0; j < dict[i].size() && k < dict[i + 1].size() &&
                       dict[i][j] == dict[i + 1][k];
         j++, k++)
      ;
    if (j < dict[i].size() && k == dict[i + 1].size()) {
      flag = 0;
      break;
    }
    if (j < dict[i].size() && k < dict[i + 1].size())
      g[dict[i][j] - 'a'].push_back(dict[i + 1][k] - 'a');
  }
  for (int i = 0; i < 26; i++) mx = max(mx, (int)g[i].size());
  for (int i = 0; flag && i < 26; i++) {
    if (!visit[i]) {
      if (topo(i) == -1) break;
    }
  }
  string ans = "";
  if (!flag) {
    ans = "Impossible";
  } else {
    while (!st.empty()) {
      ans += (st.top() + 'a');
      st.pop();
    }
  }
  return ans;
}
int main() {
  cin >> n;
  cout << printOrder();
  return 0;
}
