#include <fstream>

using namespace std;

ifstream f ("ctc.in");
ofstream g ("ctc.out");

const int nedefinit = 0;
const int stiva = 100001;

struct nod
{
    int info;
    nod *adr;
} *v[100005], *s, *comp[100005];

void adauga (int x, int y)
{
    nod *c;
    c = new nod;
    c -> info = y;
    c -> adr = v[x];
    v[x] = c;
}

void elimina (int x)
{
    nod *p;
    p = v[x];
    v[x] = v[x] -> adr;

    delete p;
}

void adauga_c (int x, int y)
{
    nod *c;
    c = new nod;
    c -> info = y;
    c -> adr = comp[x];
    comp[x] = c;
}

void elimina_c (int x)
{
    nod *p;
    p = comp[x];
    comp[x] = comp[x] -> adr;

    delete p;
}

int n, m, nr_comp = 0;

void citire ()
{
    int x, y;

    f >> n >> m;

    for (int i = 1; i <= m; i ++)
    {
        f >> x >> y;
        adauga (x, y);
    }
}

int minim (int a, int b)
{
    if (a < b)
        return a;
    return b;
}

int indecs = 0, index[100005], lowlink[100005];
bool used[100005];

void conecteaza (int node)
{
    ++ indecs;

    index[node] = lowlink[node] = indecs;
    adauga (stiva, node);

    nod *c;
    c = v[node];

    while (c)
    {
        if (index[c -> info] == nedefinit)
        {
            conecteaza (c -> info);
            lowlink[node] = minim (lowlink[node], lowlink[c -> info]);
        }
        else if (! used[c -> info])
            lowlink[node] = minim (lowlink[node], index[c -> info]);

        c = c -> adr;
    }

    if (index[node] == lowlink[node])
    {
        ++ nr_comp;

        while (v[stiva] -> info != node)
        {
            adauga_c (nr_comp, v[stiva] -> info);
            used[v[stiva] -> info] = 1;
            elimina (stiva);
        }

        adauga_c (nr_comp, v[stiva] -> info);
        used[v[stiva] -> info] = 1;
        elimina (stiva);
    }
}

void tarjan ()
{
    for (int i = 1; i <= n; i ++)
        if (index[i] == nedefinit)
            conecteaza (i);
}

void afisare ()
{
    g << nr_comp << '\n';

    for (int i = 1; i <= nr_comp; i ++)
    {
        while (comp[i])
        {
            g << comp[i] -> info << " ";
            elimina_c (i);
        }

        g << '\n';
    }
}

int main()
{
    citire ();
    tarjan ();
    afisare ();

    f.close ();
    g.close ();
    return 0;
}