#include <bits/stdc++.h>
#include <unordered_map>
#define nmax 100005
#define kmax 200005
#define MOD 1999999973
#define INF 2012345678
#define ll long long
using namespace std;
//#define fin cin
//#define fout cout

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

int n, m, nrCT;
vector <int> L[nmax], T[nmax];
bitset <nmax> viz;
int sol[nmax], lg;
int ct[nmax];

void DFSLex(int k)
{
	viz[k] = 1;
	for (int i : L[k])
		if (viz[i] == 0)
			DFSLex(i);
	sol[++lg] = k;
}

void SortTop()
{
	for (int i = 1; i <= n; i++)
		if (viz[i] == 0)
			DFSLex(i);
}

void DFS(int k)
{
	viz[k] = 1;
	for (int i : T[k])
		if (viz[i] == 0)
			DFS(i);
}

void Kosaraju()
{
	int k;
	viz.reset();
	for (int i = n; i >= 1; i--)
	{
		k = sol[i];
		if (viz[k] == 0)
		{
			DFS(k);
			nrCT++;
		}
		ct[k] = nrCT;
	}
}

int main()
{
	int i, j, x, y;
	fin >> n >> m;
	for (i = 1; i <= m; i++)
	{
		fin >> x >> y;
		L[x].push_back(y);
		T[y].push_back(x);
	}

	SortTop();
	Kosaraju();

	fout << nrCT << "\n";
	for (i = 1; i <= nrCT; i++, fout << "\n")
		for (j = 1; j <= n; j++)
			if (ct[j] == i)
				fout << j << " ";

	fin.close();
	fout.close();
	return 0;
}