#include <iostream>
#include <fstream>

#define maxim(a, b) ((a > b) ? a : b)
using namespace std;
int M, N, A[1024], B[1024], D[1024][1024], sir[1024], bst;

int main(void)
{
    int i, j;

    ifstream f("cmlsc.in");
    ofstream g("cmlsc.out");

    f >> M >> N;

    for (i = 1; i <= M; i++)
        f >> A[i];
    for (i = 1; i <= N; i++)
        f >> B[i];

    for (i = 1; i <= M; i++)
        for (j = 1; j <= N; j++)
            if (A[i] == B[j])
                D[i][j] = 1 + D[i - 1][j - 1];
            else
                D[i][j] = maxim(D[i - 1][j], D[i][j - 1]);

    for (i = M, j = N; i;)
        if (A[i] == B[j])
            sir[++bst] = A[i], --i, --j;
        else if (D[i - 1][j] < D[i][j - 1])
            --j;
        else
            --i;

    g << bst << "\n";
    for (i = bst; i; --i)
        g << sir[i];

    return 0;
}