#include <fstream>
#include <vector>
#include <bitset>
#include <stack>
using namespace std;

ifstream f("ctc.in");
ofstream g("ctc.out");

int n, m, krez;
vector<int> G[100001], GT[100001], rez[100001];
bitset<100001> viz;
stack<int> s;

void read()
{
	int x, y;
	f >> n >> m;
	for (int i = 0; i < m; i++)
	{
		f >> x >> y;
		G[x].push_back(y);
		GT[y].push_back(x);
	}
}

void kosaraju2(int i)
{
	viz[i] = 0;
	if (s.empty())
		return;
	for (auto it : GT[i])
		if (viz[it])
			kosaraju2(it);
	rez[krez].push_back(i);
}

void kosaraju1(int i)
{
	viz[i] = 1;
	for (auto it : G[i])
		if (!viz[it])
			kosaraju1(it);
	s.push(i);
}

void solve()
{
	for (int i = 1; i <= n; i++)
		if (!viz[i])
			kosaraju1(i);
	while (!s.empty())
	{
		if (viz[s.top()])
		{
			krez++;
			kosaraju2(s.top());
		}
		s.pop();
	}
}

int main()
{
	read();
	solve();
	g << krez << "\n";
	for (int i = 1; i <= krez; i++, g << "\n")
		for (auto it : rez[i]) g << it << " ";

	return 0;
}