#include<stdio.h>
int abs(int n)
{
	if (n < 0)
		n *= -1;
	return n;
}
int main()
{
	int n;
	scanf("%d", &n);
	int i;
	int h[200005], w[200005];
	for (i = 0; i < n; i++)
		scanf("%d %d", &h[i], &w[i]);
	int in[200005], out[200005];
	for (i = 0; i < 200005; i++)
		in[i] = out[i] = 0;
	for (i = 0; i < n; i++)
	{
		in[w[i]]++;
		out[h[i]]++;
	}
	int cnt = 0;
	for (i = 0; i < 200005; i++)
	{
		if (abs(in[i] - out[i]) > 1)
			cnt += 10;
		else
			cnt += abs(in[i] - out[i]);
	}
	if (cnt > 2)
	{
		printf("0\n");
		return 0;
	}
	if (cnt == 2)
	{
		printf("1\n");
		return 0;
	}
	cnt = 0;
	for (i = 0; i < 200005; i++)
		if (in[i] > 0)
			cnt++;
	printf("%d\n", cnt);
	return 0;
}