My solution

/*
 ID: bradyawn
 PROG: cf
 LANG: C++11
*/
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <fstream>
#include <vector>
#include <string>
#include <cmath>
#include <map>
#include <utility>
#include <algorithm>
#include <set>
#include <ctime>
#include <queue>
#include <stack>

//#define inf cin
//#define outf cout

using namespace std;

bool vis[26]{};

void cycle(vector<vector<int>> &top, int start, int cur, bool &check)
{
    vis[cur] = true;
    if (cur == start)
    {
        check = true;
        return;
    }
    if (check)
    {
        return;
    }
    for(int i = 0; i < top[cur].size(); i++)
    {
        cycle(top, start, top[cur][i], check);
    }
}

void dfs(vector<vector<int>> &top, stack<int> &order, int cur)
{
    vis[cur] = true;
    for (int i = 0; i < top[cur].size(); i++)
    {
        if (!vis[top[cur][i]]) dfs(top, order, top[cur][i]);
    }
    order.push(cur);
}

int main()
{
    //ifstream inf("");
    //ofstream outf("");
    //cout << setprecision(10);


    int n;
    cin >> n;

    vector<vector<int>> top(26, vector<int>());

    string prev;
    cin >> prev;
    string now;
    for (int i = 1; i < n; i++)
    {
//        now.clear();
        cin >> now;

        bool found = false;


        for (int j = 0; j < min(now.size(), prev.size()); j++)
        {
            if (now[j] != prev[j])
            {
                top[prev[j]-97].push_back(now[j]-97); //prev indexed as int, now stored as char
                found = true;
                break;
            }
        }



        if (!found && now.size() < prev.size())
        {
            cout << "Impossible" << endl;
            return 0;
        }

        prev = now;
    }

    stack<int> order;

    bool impos = false;

    for (int i = 0; i < 26 && !impos; i++)
    {
        for (int j = 0; j < top[i].size() && !impos; j++)
        {
            if (!vis[i]) cycle(top, i, top[i][j], impos);
        }
    }

    if (impos)
    {
        cout << "Impossible" << endl;
        return 0;
    }

    for (int i = 0; i < 26; i++) vis[i] = false;

    for (int i = 25; i >= 0; i--)
    {
        if (!vis[i]) dfs(top, order, i);
    }

    while (!order.empty())
    {
        cout << char(order.top()+97);
        order.pop();
    }

    cout << endl;

    return 0;

}