/*
  ID: mytbk921
  LANG: C
  TASK: wormhole
*/

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int compare(const void *a, const void *b)
{
	return *(int*)a - *(int*)b;
}

int willstuck(int n, int holes[][2], int hmap[])
{
	int i, j;
	int time, cur;
	for (i = 0; i < n; i++) {
		/* try to enter hole i */
		time = 0;
		cur = i;
		while (time < n) {
			cur = hmap[cur];
			for (j = cur+1; j < n; j++) {
				if (holes[j][1] == holes[cur][1]) {
					cur = j;
					break;
				}
			}
			if (j == n)
				break;
			else
				time++;
		}
		if (time == n)
			return 1;
	}
	return 0;
}

int nextmap(int n, int hmap[])
{
	int i, j;
	int has_next = 0;
	for (i = n-1; i >= 0; i--) {
		if (hmap[i] > i) {
			for (j = hmap[i]+1; j < n; j++) {
				if (hmap[j] == -1) {
					has_next = 1;
					hmap[hmap[i]] = -1;
					hmap[i] = j;
					hmap[j] = i;
					break;
				}
			}
			if (!has_next) {
				hmap[hmap[i]] = -1;
				hmap[i] = -1;
			}
		}
		if (has_next)
			break;
	}
	for (i++; i < n; i++) {
		if (hmap[i] == -1) {
			for (j = i+1; hmap[j] != -1; j++)
				;
			hmap[i] = j;
			hmap[j] = i;
		}
	}
	return has_next;
}

int main()
{
	FILE *fin, *fout;
	int N;
	int holes[12][2];
	int hmap[12];
	int count = 0;
	int i;

	fin = fopen("wormhole.in", "r");
	fout = fopen("wormhole.out", "w");

	fscanf(fin, "%d", &N);
	for (i = 0; i<N; i++)
		fscanf(fin, "%d%d", &holes[i][0], &holes[i][1]);
	fclose(fin);
	qsort(holes, N, sizeof(int)*2, compare);

	for (i = 0; i < N; i += 2) {
		hmap[i] = i+1;
		hmap[i+1] = i;
	}

	do {
		if (willstuck(N, holes, hmap))
			count++;
	} while (nextmap(N, hmap));

	fprintf(fout, "%d\n", count);
	fclose(fout);
	return 0;
}