#include <bits/stdc++.h>
using namespace std;
const long long M = 1e9 + 7;
const long long N = 2e5;
long long po(long long, long long);
vector<long long> e[26];
vector<long long> color;
vector<char> ans;
void dfs(long long u) {
  color[u] = 1;
  for (auto i : e[u]) {
    if (color[i] != 2) {
      if (color[i] == 1) {
        cout << "Impossible\n";
        exit(0);
      } else {
        dfs(i);
      }
    }
  }
  color[u] = 2;
  ans.push_back((u + 'a'));
}
void solve() {
  long long n;
  cin >> n;
  string s[n];
  for (long long i = 0; i < n; i++) {
    cin >> s[i];
  }
  for (long long i = 0; i < n - 1; i++) {
    long long a = s[i].length();
    long long b = s[i + 1].length();
    long long l = 0;
    bool f = 0;
    while (l < a && l < b) {
      if (s[i][l] != s[i + 1][l]) {
        e[s[i][l] - 'a'].push_back(s[i + 1][l] - 'a');
        f = 1;
        break;
      }
      l++;
    }
    if (!f && a > b) {
      cout << "Impossible\n";
      return;
    }
  }
  color.assign(26, 0);
  for (long long i = 0; i < 26; i++) {
    if (color[i] == 0) {
      dfs(i);
    }
  }
  reverse((ans).begin(), (ans).end());
  for (auto i : ans) {
    cout << i;
  }
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long t = 1;
  for (long long i = 1; i < t + 1; i++) {
    solve();
  }
  return 0;
}
long long po(long long a, long long b) {
  if (b == 0) return 1;
  long long ans = 1;
  if (b % 2 == 0) {
    ans = po(a, b / 2) % M;
    ans = (ans % M * ans % M) % M;
  } else {
    ans = po(a, (b - 1) / 2) % M;
    ans = (ans % M * ans % M * a) % M;
  }
  return ans % M;
}
