#include<fstream>
using namespace std;
struct nod { int inf; nod *adr;};
nod *v[100010],*sol[100010];
int ctc,indx=1,k,s[100010],indice[100010],val[100010],viz[100010],n,m,x,y,i;
ifstream f("ctc.in");
ofstream g("ctc.out");

void add(int i, int j,nod *v[])

 { nod *p;
   p=new nod;
   p->inf=j;
   p->adr=v[i];
   v[i]=p;
 }

void tarjan (int i)


  { nod *p;
    viz[i]=1;

    indice[i]=indx;
    val[i]=indx;
    indx++;

    s[++k]=i;

    for(p=v[i];p;p=p->adr)

    if(!indice[p->inf])

     { tarjan(p->inf);

        if(val[i]>val[p->inf])   val[i]=val[p->inf];
     }
     else if(val[i]>val[p->inf])   val[i]=val[p->inf];


     if(indice[i]==val[i])

    { int node;  ctc++;

      do{
       node=s[k];   add(ctc,node,sol);
       k--;
       }

       while(node!=i);
    }
}


int main()
{
f>>n>>m;
for(i=1;i<=m;i++) { f>>x>>y; add(x,y,v);}
for(i=1;i<=n;i++)
  if(!viz[i]) tarjan(i);
g<<ctc<<'\n';
for(i=1;i<=ctc;i++)
 { for(;sol[i];sol[i]=sol[i]->adr)
    g<<sol[i]->inf<<" ";
   g<<'\n';
 }

f.close();
g.close();
return 0;
}