#include <bits/stdc++.h>

using namespace std;

struct nod{
    int inf;
    nod *urm;
}*l[100010],*l2[100010],*r[100010],*aux;

int n,nr,s[100010],ls,idx[100010],lowlink[100010],m,t,ceva;

void df(int x){
    nod *i;
    idx[x]=lowlink[x]=++ceva;
    s[++ls]=x;
    for (i=l[x];i!=NULL;i=i->urm){
        if (!idx[i->inf]){
            df(i->inf);
            lowlink[x]=min(lowlink[x],lowlink[i->inf]);
        }
        else if (idx[i->inf]) lowlink[x]=min(lowlink[x],lowlink[i->inf]);
    }
    if (lowlink[x]==idx[x]){
        t++;
        for (;ls>=x;ls--){
            aux = new nod;
            aux->urm=r[t];
            aux->inf=s[ls];
            r[t]=aux;
        }
    }
}

int main()
{
    int i,x,y;
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    scanf("%d%d",&n,&m);
    for (i=1;i<=m;i++){
        scanf("%d%d",&x,&y);
        aux = new nod;
        aux->urm=l[x];
        aux->inf=y;
        l[x]=aux;
    }
    ceva=0;
    for (i=1;i<=n;i++ )
        if (!idx[i]) df(i);
    printf("%d\n",t);
    for (i=1;i<=t;i++){
        nod *j;
        for (j=r[i];j!=NULL;j=j->urm)
            printf("%d ",j->inf);
        printf("\n");
    }
    return 0;
}