#include <bits/stdc++.h>
#define rep(i,n) for(int i=(0);i<(n);i++)

using namespace std;

typedef long long ll;

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }

// union-find tree with size(struct)
struct UnionFind{
    vector<int> par; // 親ノード
    vector<int> rank; // ランク
	vector<int> size; // 連結成分のサイズ

    UnionFind(int n = 1) {
        init(n);
    }

    void init(int n = 1) {
        par.resize(n);
		rank.resize(n);
		size.resize(n);
        for (int i = 0; i < n; ++i){
			par[i] = i;
			rank[i] = 0;
			size[i] = 1;
		}
    }

    int find(int x) {
        if (par[x] == x)  return x;

        int r = find(par[x]);
        return par[x] = r;
    }

    bool issame(int x, int y) {
        return find(x) == find(y);
    }

    bool unite(int x, int y) {
	    x = find(x);
		y = find(y);
	    if (x == y) return false;

	    if (rank[x] < rank[y]) swap(x, y);
	    if (rank[x] == rank[y]) ++rank[x];
	    par[y] = x;
		size[x] += size[y];
	    return true;
    }

	int getSize(int x){
		return size[find(x)];
	}

	int getRank(int x){
		return rank[find(x)];
	}
};


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

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

	vector<int> b(N), c(N);
	rep(i, N) {
		cin >> b[i] >> c[i];
		b[i]--;
		c[i]--;
	}


	int col = 0;
	map<int, int> cmap;
	rep(i, N){
		if(cmap.count(c[i]) == 0){
			cmap[c[i]] = col;
			col++;
		}
	}

	UnionFind uf(col);
	map<int, vector<int>> bmap;
	rep(i, N){
		if(bmap.count(b[i]) == 0){
			bmap[b[i]].push_back(cmap[c[i]]);
		}else{
			uf.unite(bmap[b[i]].back(), cmap[c[i]]);
			bmap[b[i]].push_back(cmap[c[i]]);
		}
	}

	int box = bmap.size();
	set<int> st;
	rep(i, col) st.insert(uf.find(i));

	cout << box - st.size() << endl;
}