#include <cstdio>
#include <vector>
using namespace std;
vector <int> graf[100003];
vector <int> grafinv[100003];
vector <int> tarec[100003];
int n,m,cnt,atins[100003],aux;
int vizitat[100003];
#define DIM 10000
char buff[DIM];
int poz=0;
 
void citeste(int &numar)
{
     numar = 0;
     //cat timp caracterul din buffer nu e cifra ignor      
     while (buff[poz] < '0' || buff[poz] > '9')     
          //daca am "golit" bufferul atunci il umplu
          if (++poz == DIM) 
               fread(buff,1,DIM,stdin),poz=0;
     //cat timp dau de o cifra recalculez numarul          
     while ('0'<=buff[poz] && buff[poz]<='9')
     {
          numar = numar*10 + buff[poz] - '0';
          if (++poz == DIM) 
               fread(buff,1,DIM,stdin),poz=0;               
     }     
}
void dfs1 (int nod)
{
	vizitat[nod]=aux;
	for(int i=0;i<(int)graf[nod].size();++i)
		if(vizitat[graf[nod][i]]!=aux)
			dfs1(graf[nod][i]);
}
void dfs2 (int nod)
{
	if(vizitat[nod]==aux)
		tarec[cnt].push_back(nod),atins[nod]=1;
	for(int i=0;i<(int)grafinv[nod].size();++i)
		if(vizitat[grafinv[nod][i]]==aux && atins[grafinv[nod][i]]==0)
			dfs2(grafinv[nod][i]);
}
void ctc ()
{
	for(int i=1;i<=n;++i)
		if(atins[i]==0)
		{
			aux=i;
			dfs1(i);
			dfs2(i);
			cnt++;
		}
}
int main ()
{
	int nr1,nr2;
	freopen("ctc.in","r",stdin);
	freopen("ctc.out","w",stdout);
	citeste(n);citeste(m);//scanf("%d%d", &n, &m);
	for(int i=1;i<=m;++i)
	{
		citeste(nr1);citeste(nr2);//scanf("%d%d", &nr1, &nr2);
		graf[nr1].push_back(nr2);grafinv[nr2].push_back(nr1);
	}
	ctc();
	printf("%d\n", cnt);
	for(int i=0;i<cnt;++i)
	{
		for(int ii=0;ii<(int)tarec[i].size();++ii)
			printf("%d ", tarec[i][ii]);
		printf("\n");
	}
	return 0;
}