#include <iostream>
#include <fstream>
#include <list>
#include <stack>
#include <vector>

std::ifstream in("ctc.in");
std::ofstream out("ctc.out");

class Graf
{
    int n,size;
    std::list<int>* g;
    std::list<int> *ad;
    void SCCUtil(int u, int disc[], int low[],
                 std::stack<int> *st, bool stackMember[]);
public:
    Graf(int n);
    void addEdge(int i, int j);
    void SCC();
};

Graf::Graf(int n)
{
    this->n = n;
    ad = new std::list<int>[n+1];
    g = new std::list<int> [n+1];
    size = 0;
}

void Graf::addEdge(int i, int j)
{
    ad[i].push_back(j);
}


void Graf::SCCUtil(int u, int disc[], int low[], std::stack<int> *st,
                    bool stackMember[])
{
    static int time = 0;
    disc[u] = low[u] = ++time;
    st->push(u);
    stackMember[u] = true;
    std::list<int>::iterator i;
    for (i = ad[u].begin(); i != ad[u].end(); ++i)
    {
        int v = *i;

        if (disc[v] == -1)
        {
            SCCUtil(v, disc, low, st, stackMember);
            low[u]  = std::min(low[u], low[v]);
        }
        else if (stackMember[v] == true)
            low[u]  = std::min(low[u], disc[v]);
    }

    int w = 0;
    if (low[u] == disc[u])
    {
        size ++;
        while (st->top() != u)
        {
            w = (int) st->top();
            g[size].push_back(w);
            stackMember[w] = false;
            st->pop();
        }
        w = (int) st->top();
        g[size].push_back(w);
        stackMember[w] = false;
        st->pop();
    }
}

void Graf::SCC()
{
    int *disc = new int[n];
    int *low = new int[n];
    bool *stackMember = new bool[n];
    std::stack<int> *st = new std::stack<int>();

    for (int i = 1; i <= n; i++)
    {
        disc[i] = -1;
        low[i] = -1;
        stackMember[i] = false;
    }

    for (int i = 1; i <= n; i++)
        if (disc[i] == -1)
            SCCUtil(i, disc, low, st, stackMember);


    out << size << "\n";
    while (size){
        std::list<int>::iterator i;
        for (i = g[size].begin(); i != g[size].end(); i ++)
            out << *i << " ";
        out << "\n";
        size--;
    }
}

int main()
{

    int n,m;
    in >> n >> m;

    Graf graf(n);

    while (m){

        int i, j;
        in >> i >> j;
        graf.addEdge(i,j);

        m --;
    }

    graf.SCC();

    out.close();
    in.close();
    return 0;
}