#include <fstream>

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
struct nod
{
    int val;
    nod *urm;
};
typedef nod *pnod;
pnod p,v[100003];
void ad(int x,int y)
{
    p=new nod;
    p->val=y;
    p->urm=v[x]->urm;
    v[x]->urm=p;
}
int st[100003],ind[100003],mind[100003],comp[200003],cate,ct,index,ss;
bool instack[100003];
void dfs(int i)
{
    index+=1;
    ss+=1;
    ind[i]=index;
    mind[i]=index;
    instack[i]=1;
    st[ss]=i;
    pnod p;
    p=v[i]->urm;
    while(p)
    {
        if(ind[p->val]!=0)
        {
            if(instack[p->val] and mind[i]>mind[p->val])
                mind[i]=mind[p->val];
        }
        else
        {
            dfs(p->val);
            if(mind[i]>mind[p->val])
                mind[i]=mind[p->val];
        }
        p=p->urm;
    }
    if(ind[i]==mind[i])
    {
        cate+=1;
        while(st[ss]!=i)
        {
            ct+=1;
            comp[ct]=st[ss];
            instack[ss]=0;
            ss--;
        }
        instack[i]=0;
        ct+=1;
        comp[ct]=i;
        ss--;
        ct+=1;
        comp[ct]=0;
    }
}
int main()
{
    int i,j,x,y,n,m;
    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;
            dfs(i);
        }
    }
    g<<cate<<'\n';
    j=1;
    for(i=1;i<=cate;i++)
    {
        while(comp[j]!=0)
        {
            g<<comp[j]<<" ";
            j+=1;
        }
        j+=1;
        g<<'\n';
    }
    return 0;
}