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

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

int n, m, topo[100001], k, f[100001], nctc;
vector<int> g[100001], gt[100001], ctc[100001];

void read()
{
	int x, y;
	in >> n >> m;
	while(m--)
		in >> x >> y,
		g[x].push_back(y),
		gt[y].push_back(x);
}

void dfs(int nod)
{
	f[nod] = 1;
	for(auto i : g[nod])
		if(!f[i])
			dfs(i);
	topo[++k] = nod;
}

void sort_topo()
{
	for(int i = 1; i <= n; ++i)
		if(!f[i])
			dfs(i);
}

void dfs2(int nod)
{
	f[nod] = 2;
	ctc[nctc].push_back(nod);
	for(auto i : gt[nod])
		if(f[i] == 1)
			dfs2(i);
}

void afis()
{
	out << nctc << '\n';
	while(nctc--)
	{
		for(auto i : ctc[nctc+1])
			out << i << ' ';
		out << '\n';
	}
}

int main()
{
	read();
	sort_topo();
	for(int i = k; i > 0; --i)
		if(f[topo[i]] == 1)
			nctc++,
			dfs2(topo[i]);
	afis();
	return 0;
}