#include <fstream>

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
struct nod
{
    int val;
    nod *urm;
};
typedef nod *pnod;
#define nmax 100003
pnod v[nmax],p;
void ad(int x,int y)
{
    p=new nod;
    p->val=y;
    p->urm=v[x]->urm;
    v[x]->urm=p;
}
int n,m,index,ss;
int instack[nmax],st[nmax],ind[nmax],mind[nmax],fi[2*nmax],fiind,cate;
void ctc(int i)
{
    instack[i]=1;
    ss+=1;
    index+=1;
    st[ss]=i;
    ind[i]=mind[i]=index;
    pnod p;
    p=v[i]->urm;
    while(p)
    {
        if(ind[p->val]==0)
        {
            ctc(p->val);
            mind[i]=min(mind[i],mind[p->val]);
        }
        else
            if(instack[p->val]==1)
                mind[i]=min(mind[i],mind[p->val]);\
        p=p->urm;
    }
    if(ind[i]==mind[i])
    {
        cate+=1;

        while(st[ss]!=i)
        {
            fiind+=1;
            fi[fiind]=st[ss];
            instack[st[ss]]=0;
            ss-=1;
        }
        fiind+=1;
        fi[fiind]=i;
        instack[i]=0;
        ss-=1;
        fiind+=1;
    }
}
int main()
{
    int 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=ss=0;
            ctc(i);
        }
    }
    g<<cate<<'\n';
    for(i=1;i<=fiind;i++)
    {
        while(fi[i]!=0)
        {
            g<<fi[i]<<" ";
            i+=1;
        }
        g<<'\n';
    }
    return 0;
}