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

using namespace std;

#define NMAX 100002

int n, m;

vector <int> graf[NMAX];
int vizitat[NMAX];
int nivmin[NMAX];

int nrez;
vector <int> rez[NMAX];

int nr;
int st[NMAX];
int f[NMAX]; /// daca se afla in stiva

int niv;

void dfs(int poz) {
    int nivpoz;
    
    nivmin[poz] = niv;
    nivpoz = niv;
    niv++;
    st[nr] = poz;
    nr++;
    f[poz] = 1;
    vizitat[poz] = 1;
    for (int i:graf[poz]) {
        if (nivmin[i]==-1) {
            dfs(i);
            nivmin[poz] = min(nivmin[poz], nivmin[i]);
        }
        if (f[i]==1) {
            nivmin[poz] = min(nivmin[poz], nivmin[i]);
        }
    }
    if (nivmin[poz] == nivpoz) {
        do {
            nr--;
            rez[nrez].push_back(st[nr]);
            f[st[nr]]=0;
            nivmin[st[nr]] = niv;
        } while (st[nr]!=poz);
        nrez++;
    }
}

int main() {
    FILE *fin, *fout;
    fin = fopen("ctc.in", "r");
    fout = fopen("ctc.out", "w");
    
    int i, j, xi, xj;
    
    fscanf(fin, "%d%d", &n, &m);
    
    for (i=0; i<m; i++) {
        fscanf(fin, "%d%d", &xi, &xj);
        graf[xi].push_back(xj);
    }
    
    for (i=1; i<=n; i++) {
        nivmin[i] = -1;
    }
    
    nr = 0;
    nrez = 0;
    for (i=1; i<=n; i++) {
        if (vizitat[i]==0) {
            niv = 0;
            dfs(i);
        }
    }
    
    fprintf(fout, "%d\n", nrez);
    for (i=0; i<nrez; i++) {
        for (j=0; j<rez[i].size(); j++) {
            fprintf(fout, "%d ", rez[i][j]);
        }
        fprintf(fout, "\n");
    }
    
    fclose(fin);
    fclose(fout);
    return 0;
}