#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define endl "\n"
vector <vector <int>> g(26,vector <int> (26,0));
vector <vector <int>> col(26,vector <int> (26,0));

bool dfs(int v)
{
    col[v] = 1;
    for (auto to : g[v])
    {
        if (to == 0) continue;
        if (col[to] == 1) return true;
        if (col[to] == 0)
        {
            col[to] = 1;
            if (dfs(to)) return true;
        }
    }
    return false;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n;
    cin>>n;
    string s;
    cin>>s;

    for (int i = 1; i < n; i++)
    {
        int j = 0;
        string t;
        cin>>t;
        while (j < min(s.size(), t.size()) && s[j] == t[j])
            j++;
        if (j == t.size())
        {
            cout<<"Impossible"<<endl;
            return 0;
        }
        if (j == s.size())
        {
            t = s;
            continue;
        }
        g[s[j] - 'a'][t[j] - 'a'] = 1;

    }
    /*for (int i = 0; i < 26; i++){
        for (int j = 0; j < 26; j++)
            cout<<g[i][j]<<" ";
        cout<<endl;
    }*/
    for (int i = 0; i < 26; i++)
        if (dfs(i)) cout<<"Impossible"<<endl;


}