#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
#include <iterator>
#include <assert.h>
using namespace std;

const string file = "ctc";

const string infile = file + ".in";
const string outfile = file + ".out";

const int INF = 0x3f3f3f3f;
int N, M;
vector<vector<int> > G;

vector<int> idx;
vector<int> lowlink;
vector<bool> assigned;
vector<vector<int> > ctc;
stack<int> stiva;

void Tarjan(int i, int& c)
{
	lowlink[i] = idx[i] = c++;
	stiva.push(i);

	for(vector<int>::iterator itr = G[i].begin();
		itr != G[i].end();
		itr++)
	{
		if(idx[*itr] == 0)
		{
			Tarjan(*itr, c);
			lowlink[i] = min(lowlink[i], lowlink[*itr]);
		}
		else if(assigned[*itr] == false)
		{
			lowlink[i] = min(lowlink[i], lowlink[*itr]);
		}
	}


	if(idx[i] == lowlink[i])
	{
		vector<int> newCtc;
		int n = -1;
		while(n != i)
		{
			n = stiva.top();
			stiva.pop();
			newCtc.push_back(n);
		}
		ctc.push_back(newCtc);
	}

}

int main()
{
	fstream fin(infile.c_str(), ios::in);
	fin >> N >> M;
	G.resize(N + 1);


	idx.resize(N + 1);
	lowlink.resize(N + 1);
	assigned.resize(N + 1);

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

	int c = 1;
	for(int i = 1; i <= N; i++)
	{
		if(idx[i] == 0)
		{
			Tarjan(i, c);
		}
	}


	fstream fout(outfile.c_str(), ios::out);
	fout << ctc.size() << "\n";
	for(int i = 0; i < ctc.size(); i++)
	{
		for(vector<int>::reverse_iterator itr = ctc[i].rbegin();
			itr != ctc[i].rend();
			itr++)
		{
			fout << *itr << " ";
		}
		fout << "\n";
	}
	fout.close();
}