#include<fstream>
#include<vector>
#define min(a,b) a<b ? a : b
using namespace std;

int n, m, index = 1, nrComp = 0;
vector <int> graf[100001], S, vindex(100001, 0), lowlink(100001, 200001);
vector <int> compCurenta(100001, 0), sol[100001], viz(100001, 0);

void SCC(int nod){
	S.push_back(nod);
	vindex[nod] = index;
	lowlink[nod] = index++;
	compCurenta[nod] = 1;
	viz[nod] = 1;
	int i, adiacent;
	
	for (i = 0; i < (int) graf[nod].size(); i++){
		adiacent = graf[nod][i];
		
		if (vindex[adiacent] == 0) {
			SCC( adiacent );
			lowlink[nod] = min (lowlink[adiacent], lowlink[nod]);
		}
		else if (compCurenta[adiacent] == 1)
			lowlink[nod] = min (vindex[adiacent], lowlink[nod]);
		
	}
	
	if (lowlink[nod] == vindex[nod]){
		nrComp++;
		do {
			adiacent = S[S.size() - 1];
			S.pop_back();
			compCurenta[adiacent] = 0;
			sol[nrComp].push_back(adiacent);
		}
		while (nod != adiacent);
	}
}

int main(){
	ifstream fin ("ctc.in");
	fin >> n >> m;
	
	int i, x, y;
	for (i = 0; i < m; i++) {
		fin >> x >> y;
		graf[x].push_back(y);
	}
	
	for (i = 1; i <= n ; i++){
		if (!viz[i]) SCC(i);
	}
	
	ofstream fout("ctc.out");
	fout << nrComp <<"\n";
	for (int i = 1; i <= nrComp; i++){
		for (int j = 0; j < (int) sol[i].size(); j++) fout << sol[i][j] << " ";
		fout << "\n";
	}
	return 0;
}