//#pragma GCC optimize ("O2")
//#pragma GCC target ("avx2")
#include<bits/stdc++.h>
//#include<atcoder/all>
//using namespace atcoder;

using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define co(x) cout << (x) << "\n"
#define cosp(x) cout << (x) << " "
#define ce(x) cerr << (x) << "\n"
#define cesp(x) cerr << (x) << " "
#define pb push_back
#define mp make_pair
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define Would
#define you
#define please

const int SZ = 500000;
class UF {
public:
	int P[SZ + 1], kazu[SZ + 1];
	UF() : P() {
		rep1(i, SZ) P[i] = -1;
	}
	int find(int A) {
		if (P[A] < 0) return A;
		return P[A] = find(P[A]);
	}
	bool unite(int A, int B) {
		int a = find(A);
		int b = find(B);
		if (a == b) return false;
		if (P[a] > P[b]) swap(a, b);
		P[a] += P[b];
		kazu[a] += kazu[b];
		P[b] = a;
		return true;
	}
} uf;

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);


	int N, M;
	cin >> N >> M;

	rep1(i, N) uf.kazu[i] = 1;

	rep1(i, N) {
		int b, c;
		cin >> b >> c;
		uf.unite(b, c + 200000);
	}

	int kotae = 0;
	rep1(i, N) {
		if (uf.find(i) == i && uf.kazu[i]) {
			kotae += uf.kazu[i] - 1;
		}
	}
	co(kotae);

	Would you please return 0;
}