#include <fstream>

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
struct nod
{
    int val;
    nod *urm;
};
typedef nod *pnod;
#define nmax 100010
pnod v[nmax],p,comp[nmax],q;
int ind[nmax],pind[nmax],st[nmax];
void ad(int x,int y)
{
    p=new nod;
    p->val=y;
    p->urm=v[x]->urm;
    v[x]->urm=p;
}
bool instack[nmax];
int index,ss,numar;
void tarjan(int inc)
{
    pnod p;
    index+=1;
    ss+=1;
    ind[inc]=pind[inc]=index;
    st[ss]=inc;
    instack[inc]=1;
    p=v[inc]->urm;
    while(p)
    {
        if(ind[p->val]!=0)
        {
            if(instack[p->val] and pind[p->val]<pind[inc])
                pind[inc]=pind[p->val];
        }
        else
        {
            tarjan(p->val);
            if(pind[p->val]<pind[inc])
                pind[inc]=pind[p->val];
        }
        p=p->urm;
    }
    if(ind[inc]==pind[inc])
    {
        numar+=1;
        comp[numar]=new nod;
        comp[numar]->urm=0;
        comp[numar]->val=inc;
        q=comp[numar];
        while(st[ss]!=inc)
        {
            instack[st[ss]]=0;
            p=new nod;
            p->urm=0;
            p->val=st[ss];
            q->urm=p;
            q=p;
            ss-=1;
        }
        instack[inc]=0;
        ss-=1;
    }
}
int main()
{
    int n,m,i,x,y;
    f>>n>>m;
    for(i=1;i<=n;i++)
    {
        v[i]=new nod;
        v[i]->urm=0;
    }
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        ad(x,y);
    }
    for(i=1;i<=n;i++)
    {
        if(ind[i]==0)
        {
            index=0;
            ss=0;
            tarjan(i);
        }
    }
    g<<numar<<'\n';
    for(i=1;i<=numar;i+=1)
    {
        p=comp[i];
        while(p)
        {
            g<<p->val<<" ";
            p=p->urm;
        }
        g<<'\n';
    }
    return 0;
}