#include <stdio.h>
#include <iostream>

#define maximum(a, b) ((a > b) ? a : b)
#define maxSize 1024

using namespace std;

int M, N, A[maxSize], B[maxSize], D[maxSize][maxSize], seq[maxSize], bst;

int main()
{
    int i, j;
    
    freopen("cmlsc.in", "r", stdin);
    freopen("cmlsc.out", "w", stdout);
    
    scanf("%d %d", &M, &N);
    for ( i = 0; i < M; ++i )
         scanf("%d", &A[i]);
    for ( i = 0; i < N; ++i )
         scanf("%d", &B[i]);
         
    for ( i = 0; i < M; ++i )
    {
         for ( j = 0; i < N; ++j )
         {
             if ( A[j] == B[j] )
                D[i][j] = 1 + D[i-1][j-1];
             else
                D[i][j] = maximum(D[i-1][j], D[i][j-1]);     
         }
    }
    for (i = M, j = N; i; )
        if (A[i] == B[j])
           seq[++bst] = A[i], --i, --j;
        else if (D[i-1][j] < D[i][j-1])
             --j;
        else
            --i;  
    
    printf("%d\n", bst);
    for (i = bst; i; --i)
        printf("%d", seq[i]);
        
    return 0;
}