#include <stdio.h>

#define maxim(a,b)((a>b)? a : b)
#define FOR(i,a,b) for (i=a; i<=b; ++i)
#define NMax 1024

int M, N, A[NMax], B[NMax], D[NMax][NMax], sir[NMax], bst;

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