#include "bits/stdc++.h"
#include "atcoder/all"
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
//const bool debug = false;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	vector<int>vh(n), vw(n);
	map<int, int>mp;
	rep(i, n) {
		int h, w; cin >> h >> w;
		if (0 == mp.count(h)) mp[h] = mp.size();
		vh[i] = mp[h];
		if (0 == mp.count(w)) mp[w] = mp.size();
		vw[i] = mp[w];
	}
	dsu uf(mp.size());
	rep(i, n) uf.merge(vh[i], vw[i]);
	if (mp.size() != uf.size(0)) {
		cout << 0 << endl;
		return 0;
	}
	vector<int>in(mp.size()), out(mp.size());
	rep(i, n) {
		out[vh[i]]++;
		in[vw[i]]++;
	}
	vector<int>v(3);
	rep(i, mp.size()) {
		//cout << out[i] << " " << in[i] << endl;
		int x = out[i] - in[i];
		if (1 == x)v[0]++;
		else if (-1 == x)v[1]++;
		else if (0 == x)v[2]++;
	}
	if (mp.size() == v[2]) {
		cout << mp.size() << endl;
	}
	else if ((1 == v[0]) && (1 == v[1]) && ((mp.size() - 2) == v[2])) {
		cout << 1 << endl;
	}
	else {
		cout << 0 << endl;
	}
	return 0;
}