#include <fstream>
#include <vector>
#define NMAX 100002
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int n, nrct, poz;
vector <int> G[NMAX];
vector <int> Gt[NMAX];
vector <int> CTC[NMAX];
bool viz[NMAX];
int postordine[NMAX];

void citire();
void afisare();
void dfs(int x);
void dfst(int x);

int main()
{
    int i;
    citire();
    for (i=1; i<=n; i++){
        if (viz[i]==0){
            dfs(i);
        }
    }
    for (i=n; i>=1; i--){
        if (viz[postordine[i]]==1){
            nrct++;
            dfst(postordine[i]);
        }
    }
    afisare();
    return 0;
}

void citire(){
    int i, m, x, y;
    fin>>n>>m;
    for (i=1; i<=m; i++){
        fin>>x>>y;
        /// y intra in lista de adiacenta a lui x in G
        /// x intra in lista de adiac a lui y in Gt
        G[x].push_back(y);
        Gt[y].push_back(x);
    }
}

void afisare(){
    int i, j;
    fout<<nrct<<'\n';
    for (i=1; i<=nrct; i++){
        for (j=0; j<CTC[i].size(); j++){
            fout<<CTC[i][j]<<" ";
        }
        fout<<'\n';
    }
}

void dfs(int x){
    int i;
    viz[x]=1;
    /// parcurg lista de adiac a lui x
    for (i=0; i<G[x].size(); i++){
        if (viz[G[x][i]]==0){
            dfs(G[x][i]);
        }
    }
    postordine[++poz]=x;
}

void dfst(int x){
    int i;
    viz[x]=0;
    CTC[nrct].push_back(x);
    for (i=0; i<Gt[x].size(); i++){
        if (viz[Gt[x][i]]==1){
            dfst(Gt[x][i]);
        }
    }
}