#include<stdio.h>
#include<mem.h>
int n,ct;
int v[600];
int s[600];
int val[300],val1[300];
FILE *f,*g;


void print()
{
	int ok=1,ies=1,j,ok2=1;
	val[1]=1;
	val[2]=1;
	for(int i=1;i<=n&&ies==1;i++)
	{	for(j=1;j<=2*n-1;j++)
		       if(s[j]==i)
				ok=0;
		if(ok==1)
		{
			ies=0;
			ok2=0;
		}
		ok=1;
	}

	if(ok2==1)
	{
		memset(val1,0,300);

		for(i=1;i<=2*n-1;i++)
		{
			if(val1[s[i]]==0)
				val1[s[i]]=v[s[i]];
			else
				if(val1[s[i]]!=v[s[i]])
					ok2=0;
		}
		memset(val1,0,300);
	}


	if(s[1]==s[2*n-1]&&ok2==1)
	{
		ct++;
	/*	for(i=1;i<=2*n-1;i++)
			printf("%d ",s[i]);
		printf("\n"); */
	}
	memset(val,0,300);




}


int valid(int p)
{
	if (s[p]==s[p-1]) return 0;
	return 1;
}



void back(int p)
{
	for(int i=1;i<=n;i++)
	{
		s[p]=i;
			if(valid(p)==1)
			{
				val[s[p]]=1;
				if(p==2*n-1)
					print();
				else
					back(p+1);
			}

	}
}


int main()
{
	f=fopen("culori.in","r");
	g=fopen("culori.out","w");
	int i;
       //	printf("alooooo\n");
	fscanf(f,"%d",&n);
	for (i=1;i<=2*n-1;i++)
		fscanf(f,"%d",&v[i]);
	if(v[1]!=v[2*n-1])
		fprintf(g,"0\n");
	else
	{
		s[1]=1;
		s[2]=2;
		back(3);
		fprintf(g,"%d\n",ct);
	}



	fcloseall();
	return 0;
}