#include <fstream>
#include <algorithm>
#include <stack>
#include <vector>
#include <string.h>
using namespace std;

struct FastInputReader {
	
	
	
    int itr = 0;
	
	
	
    string content;
	
	
	
 
	
	
	
    FastInputReader(const string& file_name) {
	
	
	
        ifstream fin(file_name);
	
	
	
        content = string( (std::istreambuf_iterator<char>(fin) ),
	
	
	
                       (std::istreambuf_iterator<char>()    ) );
	
	
	
    }
	
	
	
 
	
	
	
    FastInputReader& operator>>(int& v) {
	
	
	
        v = 0;
	
	
	
        while (!((content[itr]) >= '0' and (content[itr] <= '9'))) { itr += 1; }
	
	
	
        while ((content[itr]) >= '0' and (content[itr] <= '9')) {
	
	
	
            v *= 10;
	
	
	
            v += content[itr] - '0';
	
	
	
            itr += 1;
	
	
	
        }
	
 
	
        return *this;
	
	
	
    }
	
	
	
} f("ctc.in");
	
ofstream g("ctc.out");

void tarjan(std::vector<std::vector<int>> &scc , const std::vector<int> *adj, const int src, int disc[],
		int low[], std::vector<bool> &is_on_stack, std::stack<int> &s) {
	static int time = 0;
	disc[src] = low[src] = ++time;
	s.push(src);
	is_on_stack[src] = true;

	for (auto it = adj[src].begin() ; it != adj[src].end(); ++it) {
		if (disc[*it] == -1) {
			tarjan(scc, adj, *it, disc, low, is_on_stack, s);
			low[src] = std::min(low[src], low[*it]);
		} else if (is_on_stack[*it] == true) {
			low[src] = std::min(low[src], low[*it]);
		}
	}

	if (disc[src] == low[src]) {
		std::vector<int> comp;
		int node;
		do {
			comp.push_back(node = s.top());
			s.pop();
			is_on_stack[node] = false;
		} while(node != src);

		scc.push_back(comp);
	}
}

int main() {
	//std::ifstream cin("ctc.in");
	//std::ofstream cout("ctc.out");
	//std::ios::sync_with_stdio(false);

	int n, m, src, dest;
	f >> n >> m;
	std::vector<std::vector<int>> scc;
	std::vector<int> adj[n];
	int disc[n], low[n];
	std::vector<bool> is_on_stack(n, false);
	std::stack<int> s;
	memset(disc, -1, sizeof(disc));
	memset(low, 0, sizeof(disc));
		
	for (; m ; --m) {
		f >> src >> dest;
		adj[src - 1].push_back(dest - 1);
	}

	for (int i = 0 ; i < n ; ++i) {
		if (disc[i] == -1) {
			tarjan(scc, adj, i, disc, low, is_on_stack, s);
		}
	}

	g << scc.size() << '\n';

	for (int i = 0 ; i < scc.size() ; ++i) {
		for (int j = 0 ; j < scc[i].size() ; ++j) {
			g << scc[i][j] + 1 << " ";
		}

		g << '\n';
	}
	return 0;
}