import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        HashMap<Integer, TreeSet<Integer>> counts = new HashMap<>();
        for (int i = 0; i < n; i++) {
            int b = sc.nextInt() - 1;
            int c = sc.nextInt();
            if (!counts.containsKey(c)) {
                counts.put(c, new TreeSet<>());
            }
            counts.get(c).add(b);
        }
        int ans = 0;
        UnionFindTree uft = new UnionFindTree(m);
        for (TreeSet<Integer> set : counts.values()) {
            int x = set.pollFirst();
            for (int y : set) {
                if (!uft.same(x, y)) {
                    ans++;
                    uft.unite(x, y);
                }
            }
        }
        System.out.println(ans);
    }
    
    static class UnionFindTree {
        int[] parents;
        
        public UnionFindTree(int x) {
            parents = new int[x];
            for (int i = 0; i < x; i++) {
                parents[i] = i;
            }
        }
        
        public int find(int x) {
            if (x == parents[x]) {
                return x;
            } else {
                return parents[x] = find(parents[x]);
            }
        }
        
        public boolean same(int x, int y) {
            return find(y) == find(x);
        }
        
        public void unite(int x, int y) {
            if (!same(x, y)) {
                parents[find(x)] = find(y);
            }
        }
    }
}