#include<fstream>
using namespace std;
ifstream cin("crossa.in");
ofstream cout("crossa.out");
int n,m,a[300],b[300],f[300][300];
void solve()
{
	int i,j,k,x,y;
	bool havea,haveb;
	cin>>n>>m;
	for (i=1;i<=n;i++)
		cin>>a[i];
	for (i=1;i<=m;i++)
		cin>>b[i];
	for (i=1;i<=n;i++)
		for (j=1;j<=m;j++)
		{
			f[i][j]=f[i-1][j];
			if (f[i][j]<f[i][j-1]) 
				f[i][j]=f[i][j-1];
			if (a[i]!=b[j])
			{
				havea=0;
				haveb=0;
				for (k=j-1;k>=1;k--)
				if (b[k]==a[i])
				{
					y=k;
					havea=1;
					break;
				}
				for (k=i-1;k>=1;k--)
					if (a[k]==b[j])
					{
						x=k;
						haveb=1;
						break;
					}
				if ((havea)&&(haveb)&&(f[i][j]<f[x-1][y-1]+1))
					f[i][j]=f[x-1][y-1]+1;
			}
		}
	cout<<f[n][m]*2<<endl;
}
int main(int argc, char *argv[])
{
	solve();
    return 0;
}