#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 co1[200020], co2[200020];
int main() {
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		int h, w;
		cin >> h >> w;
		co1[h]++, co2[w]++;
	}
	int co = 0, ans = 0;
	for (int i = 1; i <= 200000; i++) {
		co += abs(co1[i] - co2[i]);
		if (co1[i] != 0) {
			ans++;
		}
	}
	if (co == 0) {
		cout << ans << endl;
	}
	else if (co == 2) {
		cout << 1 << endl;
	}
	else {
		cout << 0 << endl;
	}
}