#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 l[200020] = {}, r[200020] = {};
set<int> st;
int main() {
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		int h, w;
		cin >> h >> w;
		st.insert(h);
		int m = l[w];
		if (r[h] == 0) {
			l[h]++;
		}
		else {
			r[h]--;
		}
		if (m == 0) {
			r[w]++;
		}
		else {
			l[w]--;
		}
	}
	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;
	}
}