#include <fstream>
#include <vector>
#define Nmax 100005

using namespace std;

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

vector <int> v[Nmax],vt[Nmax],ctc[Nmax];
int timp[Nmax], sw[Nmax], nrc[Nmax], nr, swt[Nmax], n, m, nrctc, ID[Nmax];

void df (int i )
{
	vector <int> :: iterator it;
	sw[i]=1;
	for (it=v[i].begin();it<v[i].end();it++)
		if (!sw[*it])
			df(*it);
	timp[++nr]=i;
}

void df2 (int i )
{
	vector <int> :: iterator  it;
	swt[i]=1;
	ctc[nrctc].push_back(i);
	for (it=vt[i].begin();it<vt[i].end();it++)
		if (!swt[*it])
			df2(*it);
}

void comp()
{
	int i,j;
	nrctc=0;
	nr=0;
	for (i=1;i<=n;i++)
		if (!sw[i])
			df(i);

	for (j=nr;j;j--)
		if (!swt[timp[j]])
			{
			nrctc++;
			df2(timp[j]);
			}
}

int main ()
{
	int i,x,y;
	f >> n >> m;
	for (i = 1; i <= m; i++)
	{
		f >> x >> y;
		v[x].push_back(y);
		vt[y].push_back(x);
	}
	comp();

	vector <int > ::iterator it;
	g << nrctc << '\n';
	for (i = 1; i <= nrctc; i++)
	{
		for (it = ctc[i].begin(); it < ctc[i].end(); it++)
			g << *it << ' ';
		g << '\n';
	}

	return 0;
}