#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],viz[100010],m,t,ceva;



void df(int x){

    nod *i;

    idx[x]=lowlink[x]=++ceva;
    viz[x]=1;
    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 (viz[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;
            viz[s[ls]]=0;
        }

    }

}



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;

}