#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

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

const int NMAX = 1e6 + 5;

int ctc;
vector<int> g[NMAX], tr[NMAX], rez[NMAX];
vector<int> viz(NMAX);
stack<int> po;

void DFS(int nod)
{
	viz[nod] = 1;
	for (size_t i = 0; i < g[nod].size(); ++i)
		if (!viz[g[nod][i]]) DFS(g[nod][i]);
	po.push(nod);
}

void DFST(int nod)
{
	viz[nod] = 0, rez[ctc].push_back(nod);
	for (size_t i = 0; i < tr[nod].size(); ++i)
		if (viz[tr[nod][i]] == 1) DFST(tr[nod][i]);
}

int main()
{
	ios::sync_with_stdio(false);
	fin.tie(0);

	int n, m;
	fin >> n >> m;

	while (m--)
	{
		int x, y;
		fin >> x >> y;

		g[x].push_back(y), tr[y].push_back(x);
	}

	for (int i = 1; i <= n; ++i)
		if (!viz[i]) DFS(i);

	while (!po.empty())
	{
		if (viz[po.top()] == 1)
		{
			++ctc;
			DFST(po.top());
		}
		po.pop();
	}

	fout << ctc << "\n";

	for (int i = 1; i <= ctc; ++i)
	{
		for (size_t j = 0; j < rez[i].size(); ++j)
			fout << rez[i][j] << " ";
		fout << "\n";
	}
	
	return 0;
}