#include <iostream>
#include <fstream>
#include <vector>
#include <deque>

using namespace std;

void strongconnect(int v,int &index, vector <int> &indexv,vector <int> &lowlink,vector <bool> &on_stack, vector < vector < int > > &vecini, deque <int> &S, vector < vector < int > > &componente){
    indexv[v] = index;
    lowlink[v] = index;
    index++;
    S.push_front(v);
    on_stack[v] = 1;
    int w;
    for( int i = 0; i < vecini[v].size(); i++ ){
        w = vecini[v][i];
        if( indexv[w] == -1 ){
            strongconnect(w, index,indexv,lowlink,on_stack,vecini,S,componente);
            if( lowlink[ w ] < lowlink[v] ){
                lowlink[v] = lowlink[w];
            }
        }
        else{
            if( on_stack[w] == 1 ){
                if( indexv[ w ] < lowlink[v] ){
                        lowlink[v] = indexv[ w ];
                }
            }
        }
    }
    if( lowlink[v] == indexv[v] ){
        vector < int > componenta;
        do{
            w = S[0];
            S.pop_front();
            on_stack[w] = 0;
            componenta.push_back(w);
        }while( w != v );
        componente.push_back(componenta);
    }
}
int main(){
    int index = 0;
    ifstream fin("ctc.in");
    ofstream fout("ctc.out");
    int nr_noduri, nr_muchii;
    fin >> nr_noduri >> nr_muchii;
    vector < vector < int > > vecini(nr_noduri+1);
    vector < int > indexv(nr_noduri+1,-1), lowlink(nr_noduri+1,0);
    vector < bool > on_stack(nr_noduri+1,0);
    vector < vector < int > > componente;
    deque < int > S;
    for( int i = 0; i < nr_muchii; i++ ){
        int intrare, iesire;
        fin >> intrare >> iesire;
        vecini[intrare].push_back(iesire);
    }
    for( int i = 1; i <= nr_noduri; i++ ){
        if( indexv[i] == -1 ){
            strongconnect(i,index,indexv,lowlink,on_stack,vecini,S, componente);
        }
    }
    fout << componente.size() << endl;
    for( int i = 0; i < componente.size(); i++ ){
        for( int j = 0; j < componente[i].size(); j++ ){
            fout << componente[i][j] << " ";
        }
        fout << endl;
    }
}