#include <fstream>
#include <vector>
#define NMAX 100007

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

int n, poz;
///graful G reprezentat prin liste de adiacenta
vector<int> G[NMAX];
///graful transpus GT reprezentat prin liste de adiacenta
vector<int> GT[NMAX];

void citire();
void afisare();
void dfs(int x);
void dfst(int x);

bool viz[NMAX];
int nr;///nuarul de componente tare conexe
vector<int> ctc[NMAX];
int postordine[NMAX];

int main()
{
    citire();
    ///parcurg dfs graful G retinand varfurile in postordine
    for (int i = 1; i <= n; i++)
    {
        if (viz[i] == 0)
        {
            dfs(i);
        }
    }
    ///parcurc postordine de la dr la st si parcurg dfs in graful transpus
    for (int i = n; i >= 1; i--)
    {
        if (viz[postordine[i]] == 1) /// acest varf este nevizitat in GT
        {
            nr++;
            dfst(postordine[i]);
        }
    }
    afisare();
    return 0;
}

void dfs(int x)
{
    viz[x] = 1;
    for (int i = 0; i < G[x].size(); i++)
    {
        if (viz[G[x][i]] == 0)
        {
            dfs(G[x][i]);
        }
    }
    postordine[++poz] = x;
}

void dfst(int x)
{
    viz[x] = 0;
    ///retin acest varf in componenta conexa curenta
    ctc[nr].push_back(x);
    for (int i = 0; i < GT[x].size(); i++)
    {
        if (viz[GT[x][i]] == 1)
        {
            dfst(GT[x][i]);
        }
    }
}

void citire()
{
    int x, y, m;
    fin >> n >> m;
    for (int i = 0; i < m; i++)
    {
        fin >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
}

void afisare()
{
    fout << nr << '\n';
    for (int i = 1; i<= nr; i++)
    {
        for (int j = 0; j < ctc[i].size(); j++)
            fout << ctc[i][j] << ' ';
        fout << '\n';
    }
}