package _1390;
import java.io.BufferedReader;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.UncheckedIOException;
import java.math.BigInteger;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Deque;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Supplier;
import java.util.regex.Pattern;
import java.util.stream.IntStream;

public class Main {
    public void exec() {
        int n = stdin.nextInt();
        int m = stdin.nextInt();
        
        int[] b = new int[n];
        int[] c = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = stdin.nextInt();
            c[i] = stdin.nextInt();
        }
        
        Map<Integer, List<Integer>> d = new HashMap<>();
        for (int i = 0; i < n; i++) {
            d.computeIfAbsent(b[i], unused -> new ArrayList<>()).add(c[i]);
        }
        
        Map<Integer, Integer> e = new HashMap<>();
        for (int i = 0; i < n; i++) {
            e.put(c[i], b[i]);
        }
        
        UnionFind uf = new UnionFind(Arrays.stream(c).max().getAsInt()+1);
        for (List<Integer> slimes : d.values()) {
            for (int i = 1; i < slimes.size(); i++) {
                uf.union(slimes.get(0), slimes.get(i));
            }
        }
        
        int count = 0;
        for (int box : d.keySet()) {
            List<Integer> slimes = d.get(box);
            if (e.get(uf.find(slimes.get(0))) != box) {
                count++;
            }
        }
        stdout.println(count);
    }
    
    public class UnionFind {
        private int[] parent;
        private int[] size;

        public UnionFind(int n) {
            this.parent = IntStream.range(0, n).toArray();
            this.size = new int[n];
            Arrays.fill(this.size, 1);
        }

        public int find(int x) {
            if (parent[x] == x) {
                return x;
            }
            parent[x] = find(parent[x]);
            return parent[x];
        }

        public boolean same(int x, int y) {
            return find(x) == find(y);
        }

        public void union(int x, int y) {
            x = find(x);
            y = find(y);
            if (x == y) {
                return ;
            }

            if (size[x] < size[y]) {
                parent[x] = y;
                size[y] += size[x];
            } else {
                parent[y] = x;
                size[x] += size[y];
            }

        }

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

    private static final Stdin stdin = new Stdin(System.in);
    private static final Stdout stdout = new Stdout(System.out);

    public static void main(String[] args) {
        try {
            new Main().exec();
        } finally {
            stdout.flush();
        }
    }

    public static class Stdin {
        private Deque<String> queue;
        private BufferedReader in;
        private Pattern space;

        public Stdin(InputStream in) {
            this.queue = new ArrayDeque<>();
            this.in = new BufferedReader(new InputStreamReader(in));
            this.space = Pattern.compile(" ");
        }

        public String nextString() {
            if (queue.isEmpty()) {
                try {
                    String line = in.readLine();
                    if (line == null) {
                        throw new EOFException();
                    }
                    space.splitAsStream(line).forEach(this.queue::addLast);
                } catch (IOException e) {
                    throw new UncheckedIOException(e);
                }
            }
            return queue.removeFirst();
        }

        public int nextInt() {
            return Integer.parseInt(nextString());
        }

        public double nextDouble() {
            return Double.parseDouble(nextString());
        }

        public long nextLong() {
            return Long.parseLong(nextString());
        }
        
        public BigInteger nextBigInteger() {
            return new BigInteger(nextString());
        }

        public String[] nextStringArray(int n) {
            String[] a = new String[n];
            for (int i = 0; i < n; i++) a[i] = nextString();
            return a;
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++) a[i] = nextInt();
            return a;
        }

        public double[] nextDoubleArray(int n) {
            double[] a = new double[n];
            for (int i = 0; i < n; i++) a[i] = nextDouble();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++) a[i] = nextLong();
            return a;
        }
        
        public BigInteger[] nexBigIntegerArray(int n) {
            BigInteger[] a = new BigInteger[n];
            for (int i = 0; i < n; i++) a[i] = nextBigInteger();
            return a;
        }
        
        public List<Integer> nextIntegerList(int n) {
            return nextList(n, this::nextInt);
        }
        
        public List<Long> nextLongList(int n) {
            return nextList(n, this::nextLong);
        }
        
        public List<Double> nextDoubleList(int n) {
            return nextList(n, this::nextDouble);
        }
        
        public List<String> nextStringList(int n) {
            return nextList(n, this::nextString);
        }
        
        public List<BigInteger> nextBigIntegerList(int n) {
            return nextList(n, this::nextBigInteger);
        }
        
        private <T> List<T> nextList(int n, Supplier<T> supplier) {
            List<T> a = new ArrayList<>();
            for (int i = 0; i < n; i++) a.add(supplier.get());
            return a;
        }
    }

    public static class Stdout {
        private PrintWriter stdout;

        public Stdout(PrintStream stdout) {
            this.stdout =  new PrintWriter(stdout, false);
        }

        public void println(Object ... objs) {
            for (int i = 0, len = objs.length; i < len; i++) {
                stdout.print(objs[i]);
                if (i != len-1) stdout.print(' ');
            }
            stdout.println();
        }

        public void flush() {
            stdout.flush();
        }
    }
}