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

using namespace std;

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

const int N = 100041;

int n, m;
vector<int> gra[N];
int idx[N], lol[N];
bool vi[N];

stack<int> staketa;
vector<vector<int>> answereta;

int indexeta = 1;

void defeseta(int a){
	staketa.push(a);
	idx[a] = indexeta++;
	lol[a] = idx[a];
	
	vi[a] = true;
	
	for(auto b : gra[a]){
		if(idx[b] == 0){
			defeseta(b);
			lol[a] = min(lol[a], lol[b]);
		}else if(vi[b]){
			lol[a] = min(lol[a], idx[b]);
		}
	}
	
	if(lol[a] == idx[a]){
		answereta.push_back({});
		vector<int> &baketa = answereta.back();
		while(staketa.top() != a){
			baketa.push_back(staketa.top());
			vi[staketa.top()] = false;
			staketa.pop();
		}
		baketa.push_back(staketa.top());
		vi[staketa.top()] = false;
		staketa.pop();
	}
}

int main(){
	// ios_base::sync_with_stdio(false);
	fin >> n >> m;
	for(int i = 0; i < m; ++i){
		int a, b;
		fin>> a >> b;
		gra[a].push_back(b);
	}
	
	for(int i = 1; i <= n; ++i){
		if(idx[i]==0)defeseta(i);
	}
	
	fout << answereta.size() << "\n";
	for(auto v : answereta){
		for(auto a : v){
			fout << a << " ";
		}
		fout << "\n";
	}
	return 0;
}