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

using namespace std;

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

struct Node{
	int index=0, lowlink=0;
	bool onstack = false;
	Node(){}
	Node(int index, int lowlink) : index(index), lowlink(lowlink){
		onstack = true;
	}
};

int n, m;
vector<int> gra[100041];
void read(){
	fin >> n >> m;
	for(int i = 0; i < m; ++i){
		int a, b;
		fin >> a >> b;
		gra[a].push_back(b);
	}
}

vector<vector<int>> components;

stack<int> s;
int index = 1;
Node nodes[100041];
void strongconnect(int a){
	s.push(a);
	Node &an = nodes[a];
	an = Node(index, index);
	index++;
	for(auto b : gra[a]){
		Node &bn = nodes[b];
		if(bn.index == 0){
			strongconnect(b);
			an.lowlink = min(an.lowlink, bn.lowlink);
		}else{
			an.lowlink = min(an.lowlink, bn.index);
		}
	}
	if(an.index == an.lowlink || s.size() == 1){
		components.push_back(vector<int>());
		vector<int> &component = components.back();
		int b;
		do{
			b = s.top();
			s.pop();
			nodes[b].onstack = false;
			component.push_back(b);
		}while(b != a);
	}
}

void tarzan(){
	for(int i = 1; i <= n; ++i){
		if(nodes[i].index == 0){
			strongconnect(i);
		}
	}
}

void write(){
	fout << components.size() << "\n";
	for(auto component : components){
		for(auto a : component){
			fout << a << " ";
		}
		fout << "\n";
	}
}

int main(){
	read();
	tarzan();
	write();
	return 0;
}