#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

typedef long long i64;

const int N = 30, M = 410, S = 1 << 11;

int n, m;
char str[N];
int tr[M][26], idx;
int dar[M], ne[M], q[M];
i64 f[N][M][S];

void insert(int id) {
    cin >> str;
    int p = 0;
    for (int i = 0; str[i]; i ++ ) {
        int v = str[i] - 'a';
        if (!tr[p][v]) tr[p][v] = ++ idx;
        p = tr[p][v];
    }
    dar[p] |= 1 << id;
}

void build() {
    int hh = 0, tt = -1;
    for (int i = 0; i < 26; i ++ ) 
        if (tr[0][i]) 
            q[ ++ tt] = tr[0][i];

    while (hh <= tt) {
        int t = q[hh ++ ];
        for (int i = 0; i < 26; i ++ ) {
            int &p = tr[t][i];
            if (!p) p = tr[ne[t]][i];
            else {
                ne[p] = tr[ne[t]][i];
                dar[p] |= dar[ne[p]];
                q[ ++ tt] = p;
            }
        }
    }
}

void dfs(int len, int j, int s) {
    if (len == n) {
        if (s == (1 << m) - 1)
            cout << str << endl;
        return ;
    }

    for (int i = 0; i < 26; i ++ ) {
        int p = tr[j][i];
        if (f[len + 1][p][s | dar[p]] && f[len + 1][p][s | dar[p]] <= 42) {
            str[len] = i + 'a';
            dfs(len + 1, p, s | dar[p]);
        }
    }
}

int main() {
    cin >> n >> m;

    for (int i = 0; i < m; i ++ ) insert(i);

    build();

    f[0][0][0] = 1;
    for (int i = 0; i <= n; i ++ ) 
        for (int j = 0; j <= idx; j ++ ) 
            for (int s = 0; s < 1 << m; s ++ ) 
                for (int k = 0; k < 26; k ++ ) {
                    int p = tr[j][k];
                    f[i + 1][p][s | dar[p]] += f[i][j][s];
                }

    i64 ans = 0;
    for (int i = 0; i <= idx; i ++ ) ans += f[n][i][(1 << m) - 1];

    cout << ans << endl;

    if (ans <= 42) dfs(0, 0, 0);

    return 0;
}