#include<fstream>
#include<vector>
#include<cstring>
using namespace std;
#define NMAX 100010

int n,m;
vector <int> g[NMAX], gt[NMAX], ctc[NMAX];
bool viz[NMAX];
int postordine[NMAX],po, nrctc;


void read()
{
	int i,x,y;

	ifstream fin("ctc.in");
	fin>>n>>m;
	for (i=1; i<=m; ++i)
	{
		fin>>x>>y;
		g[x].push_back(y);
		gt[y].push_back(x);
	}
	fin.close();
}

void parcurgere(int k)
{
	int i;

	viz[k] = 1;

	for (i=0; i<(int)g[k].size(); ++i)
		if (viz[g[k][i]] == 0)
			parcurgere(g[k][i]);

	postordine[++po] = k;
}

void parcurgere2(int k)
{
	int i;

	viz[k] = 1;
	ctc[nrctc].push_back(k);

	for (i=0; i<(int)gt[k].size(); ++i)
		if (viz[gt[k][i]] == 0)
			parcurgere2(gt[k][i]);
}

void write()
{
	int i,j;
	ofstream fout("ctc.out");

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

	fout.close();
}

int main()
{
	int i;

	read();
	for (i=1; i<=n; ++i)
		if (viz[i] == 0)
			parcurgere(i);

	memset(viz,0,n+1);
	for (i=n; i>=1; --i)
		if (viz[postordine[i]] == 0)
		{
			nrctc++;
			parcurgere2(postordine[i]);
		}

	write();

	return 0;
}