#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f("/home/mihai/Documents/C++/006CTC/ctc.in");
ofstream g("/home/mihai/Documents/C++/006CTC/ctc.out");
const int NMAX = 100005;
int n, m, nr_componente; 
int viz[NMAX], viz_back[NMAX];
vector <int> v[NMAX];
vector <int> v_back[NMAX];
vector <int> sol[NMAX];
stack <int> stiva;
void DFS1(int nod)
{
	viz[nod] = 1;
	for(int i = 0; i < v[nod].size(); i++)
		if(!viz[v[nod][i]])
			DFS1(v[nod][i]);
	stiva.push(nod);
} 

void DFS2(int nod)
{
	viz_back[nod] = nr_componente;
	stiva.pop();
	for(int i = 0; i < v_back[nod].size(); i++)
		if(!viz_back[v_back[nod][i]])
		    DFS2(v_back[nod][i]);
	sol[nr_componente].push_back(nod);
}
int main()
{
	f >> n >> m;
	while(m--)
	{
		int x, y;
		f >> x >> y;
		v[x].push_back(y);
		v_back[y].push_back(x);
	}
	for(int i = 1; i <= n; i++)
		if(!viz[i])
			DFS1(i);
	while(!stiva.empty())
	{
		nr_componente++;
		DFS2(stiva.top());
	}
	g << nr_componente << "\n";
	for(int i = 1; i <= nr_componente; i++)
	{
		for(int j = 0; j < sol[i].size(); j++)
			g << sol[i][j] << " ";
		g << "\n";
	}
}