#include <iostream>
#include <algorithm>
using namespace std;

int dg[200009], ds[200009], sz[200009];
const int m = 200000;

int uf(int n)
{
	if (ds[n] == n) return n;
	return ds[n] = uf(ds[n]);
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n; cin >> n;
	for (int i = 1; i <= m; i++) {
		ds[i] = i;
		sz[i] = 1;
	}
	for (int i = 1; i <= n; i++) {
		int a, b; cin >> a >> b;
		dg[a]++; dg[b]--;
		int ua = uf(a), ub = uf(b);
		if (ua != ub) {
			ds[ub] = ua;
			sz[ua] += sz[ub];
		}
	}
	int c = 0, s0 = 0, s1 = 0, sp = 0;
	for (int i = 1; i <= m; i++) {
		if (ds[i] == i && sz[i] > 1) {
			c++;
			sp = sz[i];
		}
		if (dg[i] == -1) s0++;
		if (dg[i] == 1) s1++;
		if (dg[i] < -1 || dg[i] > 1 || c > 1) {
			cout << 0 << '\n';
			return 0;
		}
	}
	if (s0 == 1 && s1 == 1)
		cout << 1 << '\n';
	else if (s0 == 0 && s1 == 0)
		cout << sp << '\n';
	else 
		cout << 0 << '\n';
	return 0;
}