#include <cstdio>
#include <cstring>
#include <vector>

using namespace std;

inline int next_int() {
	int d;
	scanf("%d", &d);
	return d;
}

const int V = 100001;

int n, m;
bool seen[V];
vector<int> G1[V];
vector<int> G2[V];
vector<int> order;
vector<vector<int> > scc;

void dfs1(int u) {
	if (seen[u])
		return;
	seen[u] = true;
	for (int i = G1[u].size() - 1; i >= 0; i--) {
		dfs1(G1[u][i]);
	}
	order.push_back(u);
}

void dfs2(int u) {
	if (seen[u])
		return;
	seen[u] = true;
	for (int i = G2[u].size() - 1; i >= 0; i--) {
		dfs2(G2[u][i]);
	}
	scc.back().push_back(u);
}

int main() {
	freopen("ctc.in", "r", stdin);
	freopen("ctc.out", "w", stdout);
	n = next_int();
	m = next_int();
	for (int i = 0; i < m; i++) {
		int u = next_int();
		int v = next_int();
		G1[u].push_back(v);
		G2[v].push_back(u);
	}
	for (int i = 1; i <= n; i++) {
		dfs1(i);
	}
	memset(seen, false, sizeof seen);
	for (int i = order.size() - 1; i >= 0; i--) {
		if (!seen[order[i]]) {
			scc.push_back(vector<int> ());
			dfs2(order[i]);
		}
	}
	printf("%d\n", int(scc.size()));
	for (int i = scc.size() - 1; i >= 0; i--) {
		for (int j = scc[i].size() - 1; j >= 0; j--) {
			printf("%d ", scc[i][j]);
		}
		printf("\n");
	}
	return 0;
}