#include <fstream>
#include <stdio.h>
using namespace std;
FILE *fin=fopen("cmlsc.in","r");
FILE *fout=fopen("cmlsc.out","w");
int n,m,i,p,a[1025],b[1025],mat[1025][1025],x[100001],bb;
int main()
{
    fscanf(fin,"%d%d",&n,&m);
    for(i=1;i<=n;i++)fscanf(fin,"%d",&a[i]);
    for(i=1;i<=m;i++)fscanf(fin,"%d",&b[i]);

    for(i=1;i<=n;i++)
    for(p=1;p<=m;p++)
    {
                if(a[i]==b[p]){mat[i][p]=mat[i-1][p-1]+1;}
                else mat[i][p]=max(mat[i-1][p],mat[i][p-1]);
    }
    for(i=n,p=m;i>0;)
    {
            if(a[i]==b[p])
        {
            x[++bb]=a[i];
            i--;
            p--;
        }
            else
            if (mat[i-1][p]<mat[i][p-1])
                p--;

            else
                i--;
    }
      fprintf(fout,"%d\n",mat[n][m]);
    for(i=bb;i>0;i--)
        fprintf(fout,"%d",x[i]);
    return 0;
}