#include <fstream>
#include <vector>

int N;
std::vector<int> G[200001];
std::vector<int> GT[200001];
std::vector<int> S;
std::vector<int> C[100001];

int viz[100001];

void dfsG(int k) {
	viz[k] = 1;

	for (auto& nod : G[k]) {
		if (viz[nod] == 0)
			dfsG(nod);
	}

	S.push_back(k);
}

void dfsGT(int k, int nrc) {
	viz[k] = 2;
	C[nrc].push_back(k);

	for (auto& nod : GT[k]) {
		if (viz[nod] == 1)
			dfsGT(nod, nrc);
	}
}

int main() {
	std::ifstream fin("ctc.in");
	std::ofstream fout("ctc.out");

	int M;
	fin >> N >> M;

	int x, y;

	for (int i = 0; i < M; ++i) {
		fin >> x >> y;

		G[x].push_back(y);
		GT[y].push_back(x);
	}

	fin.close();

	for (int i = 1; i <= N; ++i) {
		if (viz[i] == 0)
			dfsG(i);
	}

	int nrc = 0;

	for (auto&& it = S.rbegin(); it != S.rend(); ++it) {
		if (viz[*it] == 1) {
			++nrc;

			dfsGT(*it, nrc);
		}
	}

	fout << nrc << '\n';

	for (int i = 1; i <= nrc; ++i) {
		for (auto& nod : C[i])
			fout << nod << ' ';
		fout << '\n';
	}

	fout.close();

	return 0;
}