// CTC Tarjan

#include <fstream>
#include <iostream>
#include <vector>
#include <stack>

using namespace std;

#define NMAX 100010

class Task {

public:
	void solve() {
		read_input();
		get_result();
		print_output();
	}
private:
	vector<int> adj[NMAX];
	vector<vector<int>> ctc;
	vector<int> idx;
	vector<int> low_link;
	vector<int> in_stack;
	stack<int> st;
	int n, m;

	void read_input() {
		ifstream fin("ctc.in");
		fin >> n >> m;
		in_stack = vector<int> (n + 1, 0);
		idx = vector<int> (n + 1, -1);
		low_link = vector<int> (n + 1, 0);

		int x, y;
		for (int i = 0; i < m; ++i) {
			fin >> x >> y;
			adj[x].push_back(y);
		}
		fin.close();
	}

	void get_result() {
		int index = 0;
		for (int i = 1; i <= n; ++i) {
			if (idx[i] == -1) {
				tarjan(i, &index);
			}
		}
	}

	void tarjan(int node, int* index) {
		*index = *index + 1;
		idx[node] = *index;
		low_link[node] = *index;
		in_stack[node] = 1;
		st.push(node);

		for (int neighbour : adj[node]) {
			if (idx[neighbour] == -1) {
				tarjan(neighbour, index);
				low_link[node] = min(low_link[node], low_link[neighbour]);
			} else {
				if (in_stack[neighbour] == 1) {
					low_link[node] = min (low_link[node], idx[neighbour]);
				}
			}
		}

		if (low_link[node] == idx[node]) {
			int current;
			vector<int> new_ctc;
			while (!st.empty() && current != node) {
				current = st.top();
				st.pop();
				in_stack[current] = 0;
				new_ctc.push_back(current);
			}
			ctc.push_back(new_ctc);
		}
	}

	void print_output() {
		ofstream fout("ctc.out");
		fout << ctc.size() << "\n";
		for (vector<int> comp : ctc) {
			for (int el : comp) {
				fout << el << " ";
			}
			fout << "\n";
		}
		fout.close();
	}
};

int main() {
	Task* task = new Task();
	task->solve();
	delete task;
	return 0;
}