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

bool dfs(int v)
{
    col[v] = 1;
    for (int to = 0; to < 26; to++)
    {
        if (g[v][to] == 0)
            continue;
        if (col[to] == 1)
            return true;
        if (col[to] == 0)
        {
            if (dfs(to))
                return true;
        }
    }
    col[v] = 2;
    return false;
}

void TopSort(int v)
{
    used[v] = 1;
    for (int to = 0; to < 26; to++)
    {
        if (g[v][to] == 0 || used[to] == 1)
            continue;
        TopSort(to);
    }
    ans.push_back(v);

}

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())
        {
            s = t;
            continue;
        }
        g[s[j] - 'a'][t[j] - 'a'] = 1;

    }
    for (int i = 0; i < 26; i++)
        if (col[i] == 0 && dfs(i))
        {
            cout<<"Impossible"<<endl;
            return 0;
        }
    for (int i = 0; i < 26; i++)
        if (used[i] == 0)
        {
            TopSort(i);
        }
    reverse(ans.begin(),ans.end());
    for (int i = 0; i < 26; i++)
        cout<<(char) ('a' + ans[i]);

}