#include <bits/stdc++.h>
using namespace std;
template <class T>
T pwr(T b, T p) {
  T r = 1, x = b;
  while (p) {
    if (p & 1) r *= x;
    x *= x;
    p = (p >> 1);
  }
  return r;
}
template <class T>
T lcm(T a, T b) {
  return (a / __gcd(a, b)) * b;
}
template <class T>
T sqr(T a) {
  return a * a;
}
template <class T>
void xswap(T &x, T &y) {
  if (x != y) {
    x ^= y;
    y ^= x;
    x ^= y;
  }
}
template <typename T>
inline bool isOn(T &mask, int pos) {
  return ((mask) & (1LL << pos));
}
template <typename T>
inline T setf(T mask, int pos) {
  return mask = ((mask) & (~(1LL << pos)));
}
template <typename T>
inline T sett(T mask, int pos) {
  return mask = ((mask) | (1LL << pos));
}
template <typename T>
inline T flip(T mask, int pos) {
  return mask = ((mask) ^ (1LL << pos));
}
template <class T1>
void put(T1 e) {
  cout << e << endl;
}
template <class T1, class T2>
void put(T1 e1, T2 e2) {
  cout << e1 << " " << e2 << endl;
}
template <class T1, class T2, class T3>
void put(T1 e1, T2 e2, T3 e3) {
  cout << e1 << " " << e2 << " " << e3 << endl;
}
template <class T1, class T2, class T3, class T4>
void put(T1 e1, T2 e2, T3 e3, T4 e4) {
  cout << e1 << " " << e2 << " " << e3 << " " << e4 << endl;
}
template <class T1, class T2, class T3, class T4, class T5>
void put(T1 e1, T2 e2, T3 e3, T4 e4, T5 e5) {
  cout << e1 << " " << e2 << " " << e3 << " " << e4 << " " << e5 << endl;
}
template <class T1>
void putv(vector<T1> e1) {
  for (int i = 0; i < (int)e1.size(); i++)
    (!i ? cout << e1[i] : cout << " " << e1[i]);
  cout << endl;
}
template <class T1>
void puta(T1 arr[], int l) {
  for (int i = 0; i < l; i++) (!i ? cout << arr[i] : cout << " " << arr[i]);
  cout << endl;
}
template <class T1>
bool tk(T1 &e1) {
  return (cin >> e1 ? true : false);
}
template <class T1, class T2>
bool tk(T1 &e1, T2 &e2) {
  return (cin >> e1 >> e2 ? true : false);
}
template <class T1, class T2, class T3>
bool tk(T1 &e1, T2 &e2, T3 &e3) {
  return (cin >> e1 >> e2 >> e3 ? true : false);
}
template <class T1, class T2, class T3, class T4>
bool tk(T1 &e1, T2 &e2, T3 &e3, T4 &e4) {
  return (cin >> e1 >> e2 >> e3 >> e4 ? true : false);
}
string str[110];
vector<int> adj[110];
vector<int> ans;
int col[110];
bool add_edge(string a, string b) {
  for (int i = 0; i <= min((int)a.size(), (int)b.size()) - 1; ++i) {
    if (a[i] != b[i]) {
      int u = a[i] - 'a';
      int v = b[i] - 'a';
      adj[u].push_back(v);
      return false;
    }
  }
  if ((int)a.size() > (int)b.size()) return true;
  return false;
}
bool cycl(int u) {
  if (col[u] == 2) return true;
  if (col[u] == 1) return false;
  col[u] = 2;
  for (int i = 0; i <= (int)adj[u].size() - 1; ++i) {
    int v = adj[u][i];
    if (cycl(v)) return true;
  }
  col[u] = 1;
  return false;
}
void dfs(int u) {
  if (col[u] != 0) return;
  col[u] = 1;
  for (int i = 0; i <= (int)adj[u].size() - 1; ++i) {
    int v = adj[u][i];
    dfs(v);
  }
  ans.push_back(u);
}
int main() {
  int n;
  ans.clear();
  for (int i = 0; i <= 25; ++i) adj[i].clear();
  tk(n);
  for (int i = 0; i <= n - 1; ++i) {
    tk(str[i]);
  }
  for (int i = 0; i <= n - 1; ++i) {
    for (int j = i + 1; j <= n - 1; ++j) {
      if (add_edge(str[i], str[j])) {
        put("Impossible");
        return 0;
      }
    }
  }
  for (int i = 0; i <= 25; ++i) {
    memset(col, 0, sizeof(col));
    if (cycl(i)) {
      put("Impossible");
      return 0;
    }
  }
  memset(col, 0, sizeof(col));
  for (int i = 0; i <= 25; ++i) {
    dfs(i);
  }
  for (typeof((ans).rbegin()) it = (ans.rbegin()); it != (ans).rend(); ++it) {
    cout << (char)((*it) + 'a');
  }
  cout << endl;
  return 0;
}
