import java.io.*;
import java.util.*;

public class Main {

    public static void main(String[] args) throws IOException {
        InputReader in = new InputReader(new FileInputStream("ctc.in"));

        int N = in.nextInt();
        int M = in.nextInt();

        Graph G = new Graph(N);

        for (int i = 0; i < M; i++) {
            int u = in.nextInt();
            int v = in.nextInt();

            G.addEdge(u, v);
        }

        in.close();

        TarjanStronglyConnected TSC = new TarjanStronglyConnected(G);
        int[] components = TSC.computeStronglyConnectedComponents();

        int n = TSC.getNumberOfStronglyConnectedComponents();
        ArrayList<ArrayList<Integer>> lists = new ArrayList<ArrayList<Integer>>();

        for (int i = 0; i < n; i++) {
            lists.add(new ArrayList<Integer>());
        }

        for (int i = 1; i <= N; i++) {
            lists.get(components[i] - 1).add(i);
        }

        PrintWriter out = new PrintWriter(new FileOutputStream("ctc.out"));

        out.println(lists.size());

        for (int i = 0; i < lists.size(); i++) {
            for (int x : lists.get(i)) {
                out.printf("%d ", x);
            }
            out.printf("\n");
        }

        out.flush();
        out.close();
    }

    static class TarjanStronglyConnected {
        private final Graph G;
        private final int N;

        private final int[] index, lowlink;
        private final boolean[] onStack;
        private final Stack<Integer> stack;

        private int numberOfSCCs;
        private int[] component;
        private int _index;

        TarjanStronglyConnected(Graph graph){
            this.G = graph;
            this.N = graph.getN();

            index = new int[N + 1];
            lowlink = new int[N + 1];

            onStack = new boolean[N + 1];
            stack = new Stack<>();
        }

        private void dfs(int node){
            index[node] = _index;
            lowlink[node] = _index;
            _index++;

            onStack[node] = true;
            stack.push(node);

            for (int p = G.getHead(node); p != Graph.NIL; p = G.getNext(p)) {
                int son = G.getNeighbour(p);

                if (index[son] == -1){
                    dfs(son);
                    lowlink[node] = Math.min(lowlink[node], lowlink[son]);
                }
                else if (onStack[son])
                    lowlink[node] = Math.min(lowlink[node], index[son]);
            }

            if (index[node] == lowlink[node]){
                numberOfSCCs++;
                int w;

                do {
                    w = stack.peek();
                    onStack[w] = false;
                    stack.pop();
                    component[w] = numberOfSCCs;

                } while (w != node);
            }
        }

        int[] computeStronglyConnectedComponents(){
            component = new int[N + 1];
            _index = 0;
            numberOfSCCs = 0;

            Arrays.fill(component, -1);
            Arrays.fill(index, -1);
            Arrays.fill(onStack, false);
            stack.clear();

            for (int i = 1; i <= N; i++) {
                if (index[i] == -1)
                    dfs(i);
            }

            return component;
        }

        int getNumberOfStronglyConnectedComponents(){
            return numberOfSCCs;
        }
    }

    static class Graph{
        private static class Edge{
            int node;
            int next;

            Edge(int node, int next){
                this.node = node;
                this.next = next;
            }
        }

        final static int NIL = -1;
        private int[] head;
        private int[] degree;
        private ArrayList<Edge> graph;

        private int N;
        private int counter;

        Graph(int N){
            initialize(N);
        }

        public int getN() {
            return N;
        }

        private void initialize(final int N){
            head = new int[N];
            degree = new int[N];
            graph = new ArrayList<>();

            this.N = N;
            this.counter = 0;

            Arrays.fill(head, NIL);
            Arrays.fill(degree, 0);
        }

        void addEdge(int x, int y){
            if (!(1 <= x && x <= N)) throw new AssertionError();
            x--; y--;
            graph.add(new Edge(y, head[x]));
            head[x] = counter++;
            degree[x]++;
        }

        int getHead(int node){
            if (!(1 <= node && node <= N)) throw new AssertionError();
            node--;
            return head[node];
        }

        int getNext(int p){
            if (!(0 <= p && p < counter)) throw new AssertionError();
            return graph.get(p).next;
        }

        int getNeighbour(int p){
            if (!(0 <= p && p < counter)) throw new AssertionError();
            return graph.get(p).node + 1;
        }

        boolean isEmpty(int node){
            if (!(1 <= node && node <= N)) throw new AssertionError();
            node--;
            return head[node] == NIL;
        }

        int size(int node){
            assert 1 <= node && node <= N;
            node--;
            return degree[node];
        }

        Graph transpose(){
            Graph GT = new Graph(N);

            for (int i = 1; i <= N; i++) {
                for (int son : getNeighbours(i))
                    GT.addEdge(son, i);
            }

            return GT;
        }

        List<Integer> getNeighbours(int node){
            if (!(1 <= node && node <= N)) throw new AssertionError();

            List<Integer> list = new ArrayList<>();

            for (int p = head[node - 1]; p != NIL; p = graph.get(p).next) {
                list.add(graph.get(p).node + 1);
            }

            return list;
        }
    }

    static class InputReader{
        private BufferedReader reader;
        private StringTokenizer tokenizer;
        private InputStream inputStream;

        InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 1 << 20);
            tokenizer = null;
            inputStream = stream;
        }

        private String nextToken() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()){
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                }
                catch (IOException e){
                    throw new RuntimeException(e);
                }
            }

            return  tokenizer.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(nextToken());
        }

        String nextString(){
            return nextToken();
        }

        void close() throws IOException {
            inputStream.close();
        }
    }
}