#include <stdio.h>
#include <vector>
#include <cstring>
#include <algorithm>
#define SZ(x) ((int)(x.size()))
#define nmax 100010

using namespace std;

int n, m;
bool viz[nmax];

vector<vector<int>> answer;
vector <int> order, graph[nmax], graph2[nmax];

void dfs1(int node)
{
	viz[node] = true;
	
	for (int i = 0; i < SZ(graph[node]); i++)
		if (!viz[graph[node][i]]) dfs1(graph[node][i]);
		
	order.push_back(node);
}

void dfs2(int node)
{
	viz[node] = true;
	
	for (int i = 0; i < SZ(graph2[node]); i++)
		if (!viz[graph2[node][i]]) dfs2(graph2[node][i]);
		
	answer[answer.size() - 1].push_back(node);
}

int main()
{	
	freopen("ctc.in", "r", stdin);
	freopen("ctc.out", "w", stdout);
	
	scanf("%d %d", &n, &m);
	
	for (int i = 1; i <= m; i++) {
		
		int x, y;
		
		scanf("%d %d", &x, &y);
		
		graph[x].push_back(y);
		graph2[y].push_back(x);
	}
	
	for (int i = 1; i <= n; i++)
		if (!viz[i]) dfs1(i);
		
	memset(viz, 0, sizeof(viz));
		
	for (int i = n - 1; i >= 0; i--) {
		
		int v = order[i];
		
		if (!viz[v]) {
			
			answer.push_back(vector <int>());
			
			dfs2(v);
		}
	} 
	
	printf("%d\n", SZ(answer));
	
	for (int i = 0; i < SZ(answer); i++) {
		
		for (int j = 0; j < SZ(answer[i]); j++) printf("%d ", answer[i][j]);
		
		printf("\n");
	}
	
	return 0;
}