#include <fstream>
#include <sstream>
#include <deque>
using namespace std;

//int e_026_componente_tare_conexe()
int main() 
{
	string in_file = "ctc.in";
	string out_file = "ctc.out";

	int N, M;
	const int MAX_N = 5000;
	
	//the adjacency list and the transpose adjacency list
	deque<int> adj[MAX_N + 1], adjT[MAX_N + 1];
		
	ifstream ifs(in_file);
	ifs >> N >> M;
	for (int k = 1; k <= M; k++)
	{
		int v1, v2;
		ifs >> v1 >> v2;
		adj[v1].push_back(v2);
		adjT[v2].push_back(v1);
	}
	ifs.close();

	//plus-minus paradigm
	int components_map[MAX_N + 1];
	char plus[MAX_N + 1]; //plus (1) or minus (0) or none (-1) 
	char minus[MAX_N + 1];
	for (int v = 1; v <= N; v++) components_map[v] = plus[v] = minus[v] = 0;

	int component_id = 0;
	for (int v = 1; v <= N; v++)
	{
		//check if the current node belongs to a component
		if (components_map[v] == 0) { //if not assigned
			//perform a plus-minus node identification
			component_id++;
			components_map[v] = component_id; //assign the node to a distinct component
			//search the connex component subgraph of the current node v
			//breadth search the grapsh starting with the current node v and mark the parsed nodes with +			
			//initialize the plus-minus status of the nodes
			for (int i = 1; i <= N; i++) plus[i] = minus[i] = 0;
			deque<int> Q;
			Q.push_back(v); plus[v] = 1;
			while (!Q.empty()) {
				int v1 = Q.front();
				Q.pop_front();

				//parse the adjacency list of the node v1
				for (deque<int>::iterator it = adj[v1].begin(); it != adj[v1].end(); it++) {
					int v2 = *it;
					if (plus[v2] == 0) {
						Q.push_back(v2);  
						plus[v2] = 1;
					}
				}
			}
			//breadth search the transpose graph starting with the current node v and mark the parsed nodes with -
			Q.push_back(v); minus[v] = 1;
			while (!Q.empty()) {
				int v1 = Q.front();
				Q.pop_front();

				//parse the adjacency list of the node v1
				for (deque<int>::iterator it = adjT[v1].begin(); it != adjT[v1].end(); it++) {
					int v2 = *it;
					if (minus[v2] == 0) {
						Q.push_back(v2);
						minus[v2] = 1;
					}
				}
			}

			//find the +- nodes
			for (int i = 1; i <= N; i++) {
				if (plus[i] && minus[i]) components_map[i] = component_id;
			}
		}
	}

	int no_of_components = component_id;

	stringstream* ss = new stringstream[no_of_components + 1];
	for (int v = 1; v <= N; v++) {
		int c = components_map[v];
		ss[c] << v << " ";
	}

	ofstream ofs(out_file);
	ofs << no_of_components << endl;
	for (int c = 1; c <= no_of_components; c++) ofs << ss[c].str() << endl;
	ofs.close();

	//release the memory
	delete[] ss;

	return 0;
}