#include<fstream.h>
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(viz[p->inf])
		 if(val[i]>val[p->inf])   val[i]=val[p->inf];

  if(indice[i]==val[i])
   { int node;  ctc++;
	do{
	   node=s[k];
	   viz[node]=0;
	   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(!indice[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;
}