#include <stack>
#include <cstdio>
#include <list>
#include <set>
#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <functional>
#include <unordered_set>
#include <cstring>
#include <algorithm>
#include <cctype>
#include <string>
#include <map>
#include <cmath>
using namespace std;
#define LL long long
#define ULL unsigned long long
#define SZ(x) (int)x.size()
#define Lowbit(x) ((x) & (-x))
#define MP(a, b) make_pair(a, b)
#define MS(arr, num) memset(arr, num, sizeof(arr))
#define PB push_back
#define X first
#define Y second
#define ROP freopen("input.txt", "r", stdin);
#define MID(a, b) (a + ((b - a) >> 1))
#define LC rt << 1, l, mid
#define RC rt << 1|1, mid + 1, r
#define LRT rt << 1
#define RRT rt << 1|1
#define BitCount(x) __builtin_popcount(x)
#define BitCountll(x) __builtin_popcountll(x)
#define LeftPos(x) 32 - __builtin_clz(x) - 1
#define LeftPosll(x) 64 - __builtin_clzll(x) - 1
const double PI = acos(-1.0);
const int INF = 0x3f3f3f3f;
const double eps = 1e-8;
const int MAXN = 30 + 10;
const int MOD = 29;
const int dir[][2] = { { 1, 0 }, { 0, 1 } };
int cases = 0;
typedef pair<int, int> pii;
 
int mp[MAXN][MAXN], in[MAXN];
vector<char> ans;
const int sigma_size = 26;
 
void BFS()
{
    queue<int> Q;
    for (int i = 0; i < sigma_size; i++)
        if (in[i] == 0)
        {
            Q.push(i);
            ans.PB(i);
        }
    while (!Q.empty())
    {
        int cur = Q.front(); Q.pop();
        for (int i = 0; i < sigma_size; i++)
        {
            if (mp[cur][i])
            {
                in[i]--;
                if (in[i] == 0)
                {
                    Q.push(i);
                    ans.PB(i);
                }
            }
        }
    }
    if (SZ(ans) != sigma_size) cout << "Impossible" << endl;
    else
        for (auto &i: ans) cout << (char)(i+'a');
 
}
 
string str[110];
 
int idx(char c) { return c - 'a'; }
 
int main()
{
    //ROP;
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) cin >> str[i];
    int i, j;
    for (i = 0; i < n-1; i++)
    {
        bool flag = false;
        for (j = 0; j < min(SZ(str[i]), SZ(str[i+1])); j++)
        {
            if (str[i][j] == str[i+1][j]) continue;
            flag = true;
            int a = idx(str[i][j]), b = idx(str[i+1][j]);
            if (!mp[a][b])
            {
                mp[a][b] = 1;
                in[b]++;
            }
            break;
        }
        if (!flag && SZ(str[i]) > SZ(str[i+1]))
        {
            cout <<"Impossible" << endl;
            return 0;
        }
    }
    BFS();
    return 0;
}