#include <iostream>
#include <fstream>

using namespace std;

#define IN "cmlsc.in"
#define OUT "cmlsc.out"
#define max 1111

ifstream fin(IN);
ofstream fout(OUT);

long a[max], b[max];
long v[max][max];
long sol[max];
int m,n,s;

long maxim(long a,long b);
void citire();
void afis();
void alg();

int main()
{
 citire();
  fin.close();   
  
  alg();
  
  afis();
   fout.close();
   
return 0;   
}

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

long maxim(long a, long b)
{
 if (a>b)
  return a;
return b;
}

void afis()
{
 int i;
 
 fout<<s<<endl;    
 for (i=s; i>=1; i--)  
  fout<<sol[i];
}

void alg()
{
 int i,j;
     
 for (i=1; i<=m; i++)  
  for (j=1; j<=n; j++)  
   if (a[j]==b[i])  
    v[i][j]=v[i-1][j-1]+1;  
   else  
    v[i][j]=maxim(v[i][j-1], v[i-1][j]);  
    
  s=v[m][n];  
  
  int x=m, y=n;  
       
  for (i=1; i<=s; i++)  
  {  
    while(a[y]!=b[x])  
    {  
     if (v[x][y]==v[x][y-1])  
      y--;  
     if (v[x][y]==v[x-1][y])  
      x--;  
    }
      
   sol[i]=a[y];  
   x--;  
   y--;  
  }         
}