#include <iostream>
#include <iomanip>
#include <fstream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <vector>
#include <stack>
#include <algorithm>
using namespace std;
#define MAX 100010

vector<int> Gr[MAX], Tr[MAX];
stack<int> S;
vector<vector<int> > Ctc;
bool Visited[MAX];
int N, M;

void DFS(int X) {
	Visited[X] = 1;
	for (int i = 0; i < Gr[X].size(); i++) {
		if (!Visited[Gr[X][i]]) {
			DFS(Gr[X][i]);	
		}
	}
	S.push(X);
}

void TransposeDFS(int X) {
	Ctc[Ctc.size()-1].push_back(X);
	Visited[X] = 1;
	for (int i = 0; i < Tr[X].size(); i++) {
		if (!Visited[Tr[X][i]]) {
			TransposeDFS(Tr[X][i]);
		}
	}
}

int main() {
	int X, Y;

	freopen("ctc.in","r",stdin);
	freopen("ctc.out","w",stdout);

	scanf("%d %d", &N, &M);
	for (int i = 0; i < M; i++) {
		scanf("%d %d", &X, &Y);
		Gr[X].push_back(Y);
		Tr[Y].push_back(X);
	}
	
	for (int i = 1; i <= N; i++) {
		if (!Visited[i]) {
			DFS(i);
		}
	}
	memset(Visited, 0, sizeof(Visited));
	while (S.size() > 0) {
		X = S.top();
		S.pop();
		if (!Visited[X]) {
			Ctc.resize(Ctc.size()+1);
			TransposeDFS(X);
		}
	}
	
	printf("%d\n", Ctc.size());
	for (int i = 0; i < Ctc.size(); i++) {
		for (int j = 0; j < Ctc[i].size(); j++) {
			printf("%d ", Ctc[i][j]);
		}
		printf("\n");
	}

	return 0;
}