/*

     给出n个字符串，求是否有一个“字典序”使得n个字符串是从小到大排序

     拓扑排序

     详细解释：http://www.2cto.com/kf/201502/374966.html

 */

 #include <cstdio>

 #include <iostream>

 #include <cstring>

 #include <string>

 #include <map>

 #include <algorithm>

 #include <vector>

 #include <set>

 #include <queue>

 #include <cmath>

 using namespace std;

 const int MAXN = 1e6 + ;

 const int INF = 0x3f3f3f3f;

 char s[][];

 int in[];

 bool lin[][];

 char ans[];

 bool TopoSort(void)

 {

     queue<int> q;

     int cnt = ;

     for (int i=; i<=; ++i)

     {

         if (in[i] == )

         {

             q.push (i);

             ans[cnt++] = 'a' + i - ;

         }

     }

     while (!q.empty ())

     {

         int now = q.front ();   q.pop ();

         for (int i=; i<=; ++i)

         {

             if (lin[now][i])

             {

                 in[i]--;

                 if (in[i] == )

                 {

                     q.push (i);

                     ans[cnt++] = 'a' + i - ;

                 }

             }

         }

     }

     ans[] = '\0';

     if (cnt < )   return false;

     else    return true;

 }

 int main(void)

 {

     //freopen ("C.in", "r", stdin);

     int n;

     while (~scanf ("%d", &n))

     {

         memset (lin, false, sizeof (lin));

         memset (in, , sizeof (in));

         for (int i=; i<=n; ++i)

         {

             scanf ("%s", &s[i]);

         }

         bool flag = true;

         for (int i=; i<=n- && flag; ++i)

         {

             int len1 = strlen (s[i]);

             int len2 = strlen (s[i+]);

             bool ok = false;

             for (int j=; j<=len1- && j<=len2- && !ok; ++j)

             {

                 if (s[i][j] != s[i+][j])

                 {

                     ok = true;

                     if (!lin[s[i][j]-'a'+][s[i+][j]-'a'+])

                     {

                         in[s[i+][j]-'a'+]++;

                         lin[s[i][j]-'a'+][s[i+][j]-'a'+] = true;

                     }

                 }

             }

             if (!ok && len1 > len2) flag = false;

         }

         if (!flag)  puts ("Impossible");

         else

         {

             flag = TopoSort ();

             if (!flag)   puts ("Impossible");

             else    printf ("%s\n", ans);

         }

     }

     return ;

 }