#include <fstream>
#include <vector>
using namespace std;

ifstream fi ("ctc.in");
ofstream fo ("ctc.out");

const int dim = 100005;
int N, M, NC, S[dim], viz[dim], niv[dim], low[dim], nr;
vector <int> V[dim], R[dim];

void cit ()
{
	fi >> N >> M;
	for (int i = 0, x, y; i < M; i++)
	{
		fi >> x >> y;
		V[x].push_back (y);
	}	
}

void ctc (int n)
{
	niv[n] = low[n] = ++nr;
	S[++S[0]] = n;
	viz[n] = 1;
	
	for (int i = 0, f; i < V[n].size(); i++)
	{
		f = V[n][i];
		if (niv[f] == 0)
		{
			ctc (f);
			low[n] = min (low[n], low[f]);
		}
		else if (viz[f] == 1)
		{
			low[n] = min (low[n], niv[f]);
		}	
	}
	
	if (low[n] == niv[n])
	{
		NC++;
		while (S[S[0] + 1] != n)
		{
			viz[S[S[0]]] = 0;
			R[NC].push_back (S[S[0]]);
			S[0]--;
		}
	}
}

void afi ()
{
	fo << NC << '\n';
	for (int i = 1; i <= NC; i++)
	{
		for (int j = 0; j < R[i].size(); j++)
		{
			fo << R[i][j] << ' ';
		}
		fo << '\n';
	}
}

int main ()
{
	cit ();
	for (int i = 1; i <= N; i++)
		if (niv[i] == 0)
			ctc (i);
	afi ();
	return 0;
}