#ifdef ONLINE_JUDGE
#include <bits/stdc++.h>
#else
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <map>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <queue>
#include <climits>
#endif

using namespace std;

	// lambda : [] (int a, int b) -> bool { body return }
	// string r_str = R"(raw string)"

#define mp make_pair
#define mt make_tuple
#define eb emplace_back
#define pb push_back
#define LL long long
#define ULL unsigned long long
#define BASE 73
#define NMAX 10000
#define NMAX2 20001
#define MOD1 1000000007
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()
#define CRLINE Duxar(__LINE__);
#define SHOWME(x) cerr << __LINE__ << ": " << #x << " = " << (x) << endl;
#define ENTER putchar('\n');

int dx4[] = {-1, 0, 1, 0};
int dy4[] = {0, 1, 0, -1};

int dx8[] = {-1, -1, 0, 1, 1, 1, 0, -1};
int dy8[] = {0, 1, 1, 1, 0, -1, -1, -1};

void Duxar(int _this_line) {
#ifndef ONLINE_JUDGE
	printf("\n . . . . . . . . . . . . . Passed line - %d\n", _this_line);
#endif
}

template <class T>
void ReadNo(T &_value) {
	T _sign = 1;
	char ch;
	_value = 0;
	while(!isdigit(ch = getchar())) {
		(ch == '-') && (_sign = -1);
	}
	do {
		_value = _value * 10 + (ch - '0');
	} while(isdigit(ch = getchar()));
	_value *= _sign;
}

int N, M, level = 1;
vector <vector <int> > graph, components;
vector <int> visited, node_level, best_down;
stack <int> nodes;

void Tarjan(int iam) {
	node_level[iam] = best_down[iam] = level++;
	nodes.push(iam);
	visited[iam] = 1;
	for (auto to: graph[iam]) {
		if (visited[to] == 0) {
			Tarjan(to);
			best_down[iam] = min(best_down[iam], best_down[to]);
		}
		else if (visited[to] == 1) {
			best_down[iam] = min(best_down[iam], node_level[to]);
		}
	}
	
	if (best_down[iam] == node_level[iam]) {
		vector <int> component;
		int x;
		while (!nodes.empty() && (x = nodes.top()) != iam) {
			component.pb(x);
			visited[x] = 2;
			nodes.pop();
		}
		nodes.pop();
		component.pb(iam);
		visited[iam] = 2;
		components.pb(component);
	}
}

int main(){
	string file_input = "ctc";
#ifdef INFOARENA
	freopen((file_input + ".in").c_str(), "r", stdin);
	freopen((file_input + ".out").c_str(), "w", stdout);
#else
#ifndef ONLINE_JUDGE
	freopen("input.cpp", "r", stdin);
#endif
#endif
	
	int i, x, y;
	ReadNo(N); ReadNo(M);
	graph.resize(N + 1);
	node_level.resize(N + 1);
	best_down.resize(N + 1);
	visited.resize(N + 1);
	
	for (i = 0; i < M; ++i) {
		ReadNo(x); ReadNo(y);
		graph[x].pb(y);
	}
	
	for (i = 1; i <= N; ++i) {
		if (visited[i] == 0) {
			Tarjan(i);
		}
	}
	
	printf("%lu\n", components.size());
	for (auto component: components) {
		for (auto elem: component) {
			printf("%d ", elem);
		}
		ENTER
	}
	
	return 0;
}