#include <fstream>
#include <stack>
#include <vector>

using namespace std;
ifstream cin("ctc.in");
ofstream cout("ctc.out");

const int NMAX = 100001;

int nrCtc;
stack<int>s;
vector<int>g[NMAX];
vector<int>gt[NMAX];
vector<int>f;
vector<int>ctc[NMAX];
int n, m;

void dfsp(int nod)
{
	f[nod] = 1;
	for (auto x : g[nod])
		if (!f[x])
			dfsp(x);
	s.push(nod);
}
void dfsm(int nod)
{
	f[nod] = 2;
	ctc[nrCtc].push_back(nod);
	for (auto x : gt[nod])
		if (f[x] == 1)
			dfsm(x);
}
int main()
{
	cin >> n >> m;
	f.resize(n+1);
	for (int i = 0; i < m; i++)
	{
		int x, y;
		cin >> x >> y;
		g[x].push_back(y);
		gt[y].push_back(x);
	}
	for (int i = 1; i <= n; i++)
		if (!f[i])
			dfsp(i);
	while (!s.empty())
	{
		if (f[s.top()] == 1)
		{
			nrCtc++;
			dfsm(s.top());
		}
		s.pop();
	}
	cout << nrCtc << '\n';
	for (int i = 1; i <= nrCtc; i++,cout << '\n')
		for (int j = 0; j < ctc[i].size(); j++)
			cout << ctc[i][j] << ' ';
	return 0;
}