#include <cstdio>
#define MAXN 100001

using namespace std;

struct nod {int inf; nod* urm;};

int n, m, mrk = 0;
nod* v[MAXN];
nod* vt[MAXN];
int mark[MAXN];

void push (int x, int y) {
    nod* p;
    p = new nod;
    p->inf = y;
    p->urm = v[x];
    v[x] = p;
    p = new nod;
    p->inf = x;
    p->urm = vt[y];
    vt[y] = p;
}

void read () {
    freopen ("ctc.in", "r", stdin);
    scanf ("%d%d", &n, &m);
    int i, x, y;
    for (i=1; i<=m; ++i) {
        scanf ("%d%d", &x, &y);
        push (x, y);
    }
    fclose (stdin);
}

int nr, postord[MAXN];
bool viz[MAXN];

void DFS (int i) {
    viz[i] = 1;
    nod* p;
    p = v[i];
    while (p) {
        if (!viz[p->inf])
            DFS (p->inf);
        p = p->urm;
    }
    postord[++nr] = i;
}

void DFST (int i) {
    viz[i] = 0;
    mark[i] = mrk;
    nod* p;
    p = vt[i];
    while (p) {
        if (viz[p->inf])
            DFST (p->inf);
        p = p->urm;
    }
}

void solve () {
    int i;
    for (i=1; i<=n; ++i)
        if (!viz[i])
            DFS(i);
    for (i=n; i>0; --i)
        if (viz[postord[i]]) {
            ++mrk;
            DFST (postord[i]);
        }
}

void write () {
    freopen ("ctc.out", "w", stdout);
    printf ("%d\n", mrk);
    int i, j;
    for (i=1; i<=mrk; ++i) {
        for (j=1; j<=n; ++j)
            if (mark[j] == i)
                printf ("%d ", j);
            printf ("\n");
    }
    fclose (stdout);
}

int main () {
    read ();
    solve ();
    write ();
    return 0;
}