/*
Componente tare conexe.
*/

#include <iostream>
#include <vector>
#include <algorithm>
#include <stdio.h>

#define MAXN	100050

using namespace std;

int nr_noduri, nr_muchii, nr_comp_conexe;
vector<int> graf_init[MAXN], graf_transpus[MAXN], componente[MAXN];
vector<int> stiva, vizitat, marcat;

void df_graf_init (int u) {
	int i;
	vizitat[u] = true;
	for (i = 0; i < graf_init[u].size(); i++)
		if (vizitat[graf_init[u][i]] == false)
			df_graf_init(graf_init[u][i]);
	stiva.push_back(u);
}

void df_graf_transpus (int u, int idx_comp) {
	int i;
	marcat[u] = idx_comp;
	for (i = 0; i < graf_transpus[u].size(); i++)
		if (marcat[graf_transpus[u][i]] == 0)
			df_graf_transpus(graf_transpus[u][i], idx_comp);
}

int main () {
	freopen("ctc.in", "r", stdin);
	freopen("ctc.out", "w", stdout);

	int i, j, x, y;
	scanf("%d %d", &nr_noduri, &nr_muchii);
	for (i = 0; i < nr_muchii; i++) {
		scanf("%d %d", &x, &y);
		graf_init[x].push_back(y);
		graf_transpus[y].push_back(x);
	}

	vizitat.resize(nr_noduri);
	vizitat.assign(vizitat.size(), 0);

	for (i = 1; i <= nr_noduri; i++)
		if (vizitat[i] == false)
			df_graf_init(i);

	marcat.resize(nr_noduri);
	marcat.assign(marcat.size(), 0);

	nr_comp_conexe = 0;
	while (stiva.size() > 0) {
		if (marcat[stiva.back()] == 0) {
			nr_comp_conexe++;
			df_graf_transpus(stiva.back(), nr_comp_conexe);
		}
		stiva.pop_back();
	}

	for (i = 1; i <= nr_noduri; i++)
		componente[marcat[i]].push_back(i);

	printf("%d\n", nr_comp_conexe);

	for (i = 1; i <= nr_comp_conexe; i++) {
		for (j = 0; j < componente[i].size(); j++)
			printf("%d ", componente[i][j]);
		printf("\n");
	}

	return 0;
}