using namespace std;
#include<iostream>
#include<cstdio>
struct nod{
    int info;
    nod *next;
};

nod *G[50005], *Gt[50005], *CTC[50005];
int n,ord[50005],timp,v[50005],vt[50005],NR[50005],nr,nrc;

void citire()
{
    int i,m,a,b;
    nod *p;
    scanf("%d%d", &n, &m);
    for(i=1;i<=n;i++)
        G[i]=Gt[i]=CTC[i]=NULL;
    for(i=1;i<=m;i++)
    {
        scanf("%d%d", &a, &b);
        p=new nod;
        p->info=b;
        p->next=G[a];
        G[a]=p;
        p=new nod;
        p->info=a;
        p->next=Gt[b];
        Gt[b]=p;
    }
}

void dfs(int varf)
{
    v[varf]=1;
    for(nod *p=G[varf];p;p=p->next)
        if(v[p->info]==0)
            dfs(p->info);
    ord[++timp]=varf;
}

void sort(int nrc)
{
    int aux;
    nod *p=CTC[nrc];
    while(p->next->info>p->info);
    {
        aux=p->next->info;
        p->next->info=p->info;
        p->info=aux;
        p=p->next;
    }
}

void dfst(int varf,int nrc)
{
    //printf("%d ",varf);
    vt[varf]=nrc;
    nod *p=new nod;
    p->info=varf;
    p->next=CTC[nrc];
    CTC[nrc]=p;
    //sort(nrc);
    for(p=Gt[varf]; p ; p=p->next)
        if(vt[p->info]==0)
            dfst(p->info,nrc);
}

void kosaraju()
{
    int i;
    nod *p;
    for(i=1;i<=n;i++)
        if(v[i]==0)
            dfs(i);
    for(i=timp;i>0;i--)
        if(vt[ord[i]]==0)
            dfst(ord[i],++nrc), printf("\n");
}

void write()
{
    nod *p;
    freopen("retele.out","w",stdout);
    printf("%d\n",nrc);
    int i;
    for(i=1;i<=nrc;i++)
    {
        printf("%d: ",i);
        for(p=CTC[i]; p ; p = p->next)
            printf("%d ", p -> info);
        printf("\n");
    }

}

void Afis(nod *G[]){
    for(int i=1;i<=n;++i){
        printf("%d : ",i);
        for(nod *p=G[i]; p ; p=p->next)
            printf("%d ",p->info);
        printf("\n");
    }
}

int main()
{
    freopen("retele.in","r",stdin);
    citire();
    //Afis(G);
    //Afis(Gt);
    kosaraju();
    write();
    return 0;
}