//
//  main.cpp
//  Componente_tare_conexe
//
//  Created by Alex Petrache on 18/05/14.
//  Copyright (c) 2014 Alex Petrache. All rights reserved.
//

#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <set>
#define N_MAX 100009

using namespace std;

vector<int> V[N_MAX];
stack<int> S;
set<int> Sol[N_MAX];
int n,m,nivel,ctc;
int Niv[N_MAX], Low[N_MAX], viz[N_MAX], iesit[N_MAX];

void dfs(int nod){
    nivel++;
    Niv[nod]=Low[nod]=nivel;
    S.push(nod);
    viz[nod]=1;
    
    for(int i=0;i<V[nod].size();i++){
        if(!viz[V[nod][i]])
            dfs(V[nod][i]);
        if(iesit[V[nod][i]]==0)
            Low[nod]=min(Low[nod],Low[V[nod][i]]);
    }
    
    if(Niv[nod]==Low[nod]){
        ctc++;
        while(S.top()!=nod){
            Sol[ctc].insert(S.top());
            iesit[S.top()]=1;
            S.pop();
        }
        Sol[ctc].insert(S.top());
        iesit[S.top()]=1;
        S.pop();
    }
    
}

int main(int argc, const char * argv[])
{
    int i,x,y;
//    ifstream f("/Users/alexpetrache/Documents/Programare/Xcode/Componente_tare_conexe/Componente_tare_conexe/ctc.in");
    ifstream f("ctc.in");
    ofstream g("ctc.out");
    f>>n>>m;
    for(i=1;i<=m;i++){
        f>>x>>y;
        V[x].push_back(y);
    }
    
    for(i=1;i<=n;i++){
        if(!viz[i])
            dfs(i);
    }
    
    g<<ctc<<'\n';
    for(i=1;i<=ctc;i++){
        for(set<int>::iterator it = Sol[i].begin() ; it != Sol[i].end() ; it++ )
            g<<(*it)<<" ";
        g<<'\n';
    }
    
    return 0;
}