#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
int h[200020], w[200020];
int l[200020] = {}, r[200020] = {};
set<int> st;
int main() {
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> h[i] >> w[i];
		if (h[i] == w[i]) {
			l[h[i]]++;
			r[w[i]]++;
		}
	}
	for (int i = 0; i < n; i++) {
		if (h[i] != w[i]) {
			st.insert(h[i]);
			int m = l[w[i]];
			if (r[h[i]] == 0) {
				l[h[i]]++;
			}
			else {
				r[h[i]]--;
			}
			if (m == 0) {
				r[w[i]]++;
			}
			else {
				l[w[i]]--;
			}
		}
	}
	int l1 = 0, r1 = 0;
	for (int i = 1; i <= 200000; i++) {
		l1 += l[i];
		r1 += r[i];
	}
	if (l1 == 0 && r1 == 0) {
		cout << st.size() << endl;
	}
	else if (l1 == 1 && r1 == 1) {
		cout << 1 << endl;
	}
	else {
		cout << 0 << endl;
	}
}