import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Set;
import java.util.stream.Collectors;

public class Main {
    static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static final BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

    public static void main(String[] args) {
        try {
            IRunner runner = new Runner(br, bw);
            runner.run();
            runner.flush();

            br.close();
            bw.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

class Runner implements IRunner {
    final IReader reader;
    final BufferedWriter bw;
    final StringBuilder sb = new StringBuilder();

    final int N, V = 1;
    final Map<Integer, Set<Integer>> graph = new HashMap<>();

    Runner(BufferedReader br, BufferedWriter bw) {
        this.reader = new Reader(br);
        this.bw = bw;

        try {
            this.N = reader.readInts()[0];
            reader.skipLine();
            reader.lines().forEach(line -> {
                var parts = line.split(" ");
                int source = Integer.parseInt(parts[0]);
                int dest = Integer.parseInt(parts[1]);
                graph.computeIfAbsent(source, k -> new HashSet<>()).add(dest);
                graph.computeIfAbsent(dest, k -> new HashSet<>()).add(source);
            });
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void flush() {
        try {
            bw.write(sb.toString());
            bw.flush();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void run() {
        Queue<Integer> queue = new ArrayDeque<>();
        boolean[] visited = new boolean[N + 1];
        queue.add(V);

        while (!queue.isEmpty()) {
            int v = queue.poll();
            if (visited[v])
                continue;
            bfs(v, visited, queue);
        }

        int count = -1;
        for (int i = 1; i <= N; ++i) {
            if (visited[i]) {
                ++count;
            }
        }
        sb.append(count).append("\n");
    }

    private void bfs(int v, boolean[] visited, Queue<Integer> queue) {
        visited[v] = true;

        Iterator<Integer> neighbors = graph.getOrDefault(v, new HashSet<>()).iterator();
        if (!neighbors.hasNext()) {
            return;
        }
        while (neighbors.hasNext()) {
            queue.add(neighbors.next());
        }
    }

}

class Reader implements IReader {
    private BufferedReader br;

    public Reader(BufferedReader br) {
        this.br = br;
    }

    @Override
    public void skipLine() throws IOException {
        br.readLine();
    }

    @Override
    public int[] readInts() throws IOException {
        String[] tokens = br.readLine().split(" ");
        int[] ints = new int[tokens.length];
        for (int i = 0; i < tokens.length; ++i) {
            ints[i] = Integer.parseInt(tokens[i]);
        }
        return ints;
    }

    @Override
    public List<Integer> readIntegers() throws IOException {
        return Arrays.stream(readInts()).boxed().collect(Collectors.toList());
    }

    @Override
    public List<String> lines() throws IOException {
        return br.lines().collect(Collectors.toList());
    }

    @Override
    public String line() throws IOException {
        return br.readLine();
    }
}

interface IRunner {
    void run();

    void flush();
}

interface IReader {
    void skipLine() throws IOException;

    List<Integer> readIntegers() throws IOException;

    int[] readInts() throws IOException;

    List<String> lines() throws IOException;

    String line() throws IOException;
}