#include <bits/stdc++.h>
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");

class Graph
{
private:
    int numberOfNodes, numberOfEdges;
    vector<vector<int>> listOfNeighbours;
    bool isDirected;

public:
    Graph(int numberOfNodes = 0, int numberOfEdges = 0, bool isDirected = 0)
    {
        this->numberOfNodes = numberOfNodes;
        this->numberOfEdges = numberOfEdges;
        this->isDirected = isDirected;
    }
    ~Graph()
    {
        this->numberOfEdges = 0;
        this->numberOfNodes = 0;
    }
    void setNumberOfEdges(int &);
    void setNumberOfNodes(int &);
    void setEdges(int, int);
    int getNumberOfNodes();
    int getNumberOfEdges();
    void readEdges(istream &in);
    void printListOfNeighbours(ostream &out);
    int numberOfConnectedComponents(bool[]);
    void BFS(int, bool[], int[]);
    void topologicalSorting(bool[], stack<int> &);
    void stronglyConnectedComponents(int, bool[], int &, vector<vector<int>> &, stack<int> &, vector<vector<int>> &);

private:
    void DFS(int, bool[]);
    void topologicalSortingDFS(int, bool[], stack<int> &);
    void stronglyConnectedComponentsDFS(int, bool[], vector<vector<int>>, int, vector<vector<int>> &);
};

void Graph::setNumberOfEdges(int &m)
{
    numberOfEdges = m;
}
void Graph::setNumberOfNodes(int &n)
{
    numberOfNodes = n;
}
void Graph::setEdges(int firstNode, int secondNode)
{
    listOfNeighbours[firstNode].push_back(secondNode);
}
int Graph::getNumberOfNodes()
{
    return numberOfNodes;
}
int Graph::getNumberOfEdges()
{
    return numberOfEdges;
}
void Graph::readEdges(istream &in)
{
    int firstNode, secondNode;
    listOfNeighbours.resize(numberOfNodes + 2);
    for (int i = 0; i < this->numberOfEdges; i++)
    {
        in >> firstNode >> secondNode;
        setEdges(firstNode, secondNode);
        if (!isDirected)
            setEdges(secondNode, firstNode);
    }
}
void Graph::printListOfNeighbours(ostream &out)
{
    for (int i = 1; i < this->listOfNeighbours.size() - 1; i++)
    {
        out << i << ": ";
        for (int j = 0; j < listOfNeighbours[i].size(); j++)
            out << this->listOfNeighbours[i][j] << " ";
    }
}
void Graph::DFS(int node, bool visited[])
{

    // int visited[listOfNeighbours.size()];
    visited[node] = 1;
    //out<<node<<" ";
    for (int neighbour : listOfNeighbours[node])
    {
        // out<<neighbour<<endl;
        if (!visited[neighbour])
            DFS(neighbour, visited);
    }
}
int Graph::numberOfConnectedComponents(bool visited[])
{
    int numberOfConnectedComponents = 0;
    for (int i = 1; i <= this->numberOfNodes; i++)
    {
        if (!visited[i])
        {
            // out << numberOfNodes << endl;
            numberOfConnectedComponents++;
            DFS(i, visited);
        }
    }
    return numberOfConnectedComponents;
}

void Graph::BFS(int sourceNode, bool visited[], int distance[])
{

    queue<int> queueBFS;
    queueBFS.push(sourceNode);
    visited[sourceNode] = 1;
    distance[numberOfNodes] = {0};
    while (!queueBFS.empty())
    {
        for (int node : listOfNeighbours[queueBFS.front()])
        {
            if (!visited[node])
            {
                visited[node] = 1;
                queueBFS.push(node);
                distance[node] = distance[queueBFS.front()] + 1;
            }
        }
        queueBFS.pop();
    }
    for (int node = 1; node <= numberOfNodes; node++)
    {
        if (sourceNode != node && distance[node] == 0)
            out << "-1 ";
        else
            out << distance[node] << " ";
    }
}

void Graph::topologicalSortingDFS(int node, bool visited[], stack<int> &stack)
{
    visited[node] = 1;
    for (int neighbour : listOfNeighbours[node])
    {
        if (!visited[neighbour])
            topologicalSortingDFS(neighbour, visited, stack);
    }
    stack.push(node);
}

void Graph::topologicalSorting(bool visited[], stack<int> &stack)
{
    for (int i = 1; i <= this->numberOfNodes; i++)
    {
        if (!visited[i])
            topologicalSortingDFS(i, visited, stack);
    }

    while (!stack.empty())
    {
       out << stack.top() << " ";
        stack.pop();
   }
}
void Graph::stronglyConnectedComponentsDFS(int node, bool visited[], vector<vector<int>> listOfNeighboursT, int numberOfSCC, vector<vector<int>> &solution)
{
    visited[node] = 0;
    for (int neighbour : listOfNeighboursT[node])
        if (visited[neighbour])
            stronglyConnectedComponentsDFS(neighbour, visited, listOfNeighboursT, numberOfSCC, solution);

    solution[numberOfSCC].push_back(node);
}

void Graph::stronglyConnectedComponents(int node, bool visited[], int &numberOfSCC, vector<vector<int>> &solution, stack<int> &stack, vector<vector<int>> &listOfNeighboursT)
{

    for (int i = 1; i <= numberOfNodes; i++)
        for (int j : listOfNeighbours[i])
            listOfNeighboursT[j].push_back(i);

    for (int i = 1; i <= numberOfNodes; i++)
        if (!visited[i])
            topologicalSortingDFS(i, visited, stack);
    // if(sstack.empty()) out<<"a";
    while (!stack.empty())
    {
        int top = stack.top();
        stack.pop();
        if (visited[top])
        {
            numberOfSCC++;
            stronglyConnectedComponentsDFS(top, visited, listOfNeighboursT, numberOfSCC, solution);
        }
    }
    out << numberOfSCC << '\n';
    for (int i = 1; i <= numberOfSCC; i++)
    {
        for (int j : solution[i])
            out << j << " ";
        out << '\n';
    }
}
int main()
{
    int numberOfNodes, numberOfEdges; //, sourceNode;
    in >> numberOfNodes >> numberOfEdges;
    Graph Gr(numberOfNodes, numberOfEdges, 1);
    Gr.readEdges(in);
    bool visited[numberOfNodes + 1] = {0};
    //int distance[numberOfNodes + 1] = {0};
    stack<int> stack;
    int numberOfSCC = 0;
    vector<vector<int>> solution(numberOfNodes + 2);
    vector<vector<int>> listOfNeighboursT(numberOfNodes + 2);
   // listOfNeighboursT.resize(numberOfNodes + 2);
    //solution.resize(numberOfNodes + 2);
    Gr.stronglyConnectedComponents(1, visited, numberOfSCC, solution, stack, listOfNeighboursT);
    return 0;
}