#include <bits/stdc++.h>
using namespace std;

ifstream fin("cmlsc.in");
ofstream fout("cmlsc.out");

char a[1030], b[1030];
int dp[1030][1030], n, m;

int main()
{
    int i, j;
    fin >> n >> m;
    for (i = 1; i <= n; i++)
        fin >> a[i];
    for (i = 1; i <= m; i++)
        fin >> b[i];


    for (i = n; i >= 1; i--)
        for (j = m; j >= 1; j--)
            if (a[i] == b[j])
                dp[i][j] = 1 + dp[i+1][j+1];
            else
            dp[i][j] = max(dp[i+1][j],dp[i][j+1]);

    fout << dp[1][1] << "\n";
    i = j = 1;
    while (i <= n && j <= m)
    {
        if (a[i] == b[j])
        {
            fout << a[i] << " ";
            i++; j++;
        }
        else if (dp[i+1][j] >= dp[i][j+1])
                    i++;
        else j++;
    }
    return 0;
}