#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

const int NMAX = 1e5 + 5;
vector < int > g[NMAX], gt[NMAX], ctc[NMAX], s;
int viz[NMAX];
int n, m, nr;

void dfs1(int nod){
	viz[nod] = 1;
	for(int i : g[nod])
		if(!viz[i])
			dfs1(i);
	s.push_back(nod);
}

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

int main(){
	fin >> n >> m;
	for(int i = 0, x, y; i < m; i++){
		fin >> x >> y;
		g[x].push_back(y);
		gt[y].push_back(x);
	}
	fin.close();
	for(int i = 1; i <= n; i++)
		if(!viz[i])
			dfs1(i);
	for(int i = n - 1; i >= 0; i--)
		if(viz[s[i]] == 1){
			dfs2(s[i]);
			nr++;
		}
	fout << nr << '\n';
	for(int i = 0; i < nr; i++){
		for(int j : ctc[i])
			fout << j << ' ';
		fout << '\n';
	}
	fout.close();
	return 0;
}