//kosaraju-sharir
#include <fstream>
#include <vector>
#define NMAX 100002

using namespace std;

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

vector <int> G[NMAX];
vector <int> GT[NMAX];
vector <int> CTC[NMAX];

int n, m, poz, nr, i;
bool uz[NMAX];
int postordine[NMAX];


void citire();
void DFS(int x);
void DFST(int x);
void afisare();

int main()
{
    citire();
    for (i=1;i<=n;i++)
        if (uz[i]==0) DFS(i);

    for (i=n;i>0;i--)
        if (uz[postordine[i]])
        {
            nr++;
            DFST(postordine[i]);
        }
    afisare();
    return 0;
}


void DFS(int x)
{
    int i;
    uz[x]=1;
    //parcurg lista de a diacenta a lui x
    for (i=0; i<G[x].size(); i++)
        if (uz[G[x][i]]==0)
            DFS(G[x][i]);
    postordine[++poz]=x;

}

void DFST(int x)
{
    int i;
    uz[x]=0;
    CTC[nr].push_back(x);
    //parcurg lista de a diacenta a lui x
    for (i=0; i<GT[x].size(); i++)
        if (uz[GT[x][i]]==1)
            DFST(GT[x][i]);

}

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

void citire()
{
    int i, x, y;
    f>>n>>m;
    for (i=0;i<m;i++)
    {
        f>>x>>y;
        //y intra in lista de adiacenta a vf x
        G[x].push_back(y);
        //x intra in lista de adiacenta a vf y in transpusa
        GT[y].push_back(x);

    }
}