#include<cstdio>
#include<algorithm>
#define Nmx 1000001

using namespace std;

int viz[Nmx],n,m,pre[Nmx],nr,nrs;
struct nod
{
    int inf;
    nod *urm;
};
nod *G[Nmx],*GT[Nmx];

struct ds
{
    int p,ind;
};
ds sol[Nmx];

struct cmp
{
    bool operator()(const ds &a,const ds &b)
    {
        return a.p<b.p;
    }
};

void add(int x,int y)
{
    nod *aux=new nod;
    aux->inf = y;
    aux->urm = G[x];
    G[x] = aux;
}
void addt(int x,int y)
{
    nod *aux=new nod;
    aux->inf = y;
    aux->urm = GT[x];
    GT[x] = aux;
}

void citire()
{
    int x,y;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;++i)
    {
        scanf("%d%d",&x,&y);
        add(x,y);
        addt(y,x);
    }
}

void dfs(int x)
{
    viz[x]=1;
    for(nod *p=G[x];p;p=p->urm)
        if(!viz[p->inf])
            dfs(p->inf);
    pre[++nr]=x;
}

void dfst(int x)
{
    viz[x]=0;
    sol[x].p=nrs;
    for(nod *p=GT[x];p;p=p->urm)
        if(viz[p->inf])
            dfst(p->inf);
}

int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    citire();
    for(int i=1;i<=n;++i)
    {
        if(!viz[i])
            dfs(i);
        sol[i].ind=i;
    }
    for(int i=n;i>=1;--i)
        if(viz[pre[i]])
        {
            ++nrs;
            dfst(pre[i]);
        }
    sort(sol+1,sol+n+1,cmp());
    printf("%d\n",nrs);
    int j=1;
    for(int i=1;i<=nrs;++i)
    {
        printf("%d",sol[j].ind);
        int ji=j;j++;
        while(j<=n&&sol[j].p==sol[ji].p)
        {
            printf(" %d",sol[j].ind);
            ++j;
        }
        printf("\n");
    }
    return 0;
}