#include <iostream>
#include <fstream>
using namespace std;
  
ifstream fin("ctc.in");
ofstream fout("ctc.out");
  
struct Nod{int inf; Nod* leg;};
typedef Nod* nod;
  
nod a[100001],b[100001],s,c[100002];
  
int n,m,k;
bool viz[100001],viz2[100001];
void afisare(nod q)
{
    if(q){fout<<q->inf<<" "; afisare(q->leg);}
    else fout<<endl;
}
  
void adaug(nod &q, int x)
{
    nod p=new Nod;
    p->inf=x;
    p->leg=q;
    q=p;
}
  
void parc(int i)
{
    nod j;
    viz[i]=1;
    for(j=a[i]; j; j=j->leg) 
       if (!viz[j->inf])
         parc(j->inf);
    adaug(s,i);
}
  
void parc2(int i)
{
    viz2[i]=1;
    adaug(c[k],i);
    for(nod j=b[i]; j; j=j->leg) if (!viz2[j->inf]) parc2(j->inf);
}
  
int main()
{
    int i,j,x,y;
    fin>>n>>m;
    for(i=1; i<=m; i++)
    {
        fin>>x>>y;
        adaug(a[x],y);
        adaug(b[y],x);
    }
    for(i=1; i<=n; i++)
        if(!viz[i])
            parc(i);
    while(s)
    {
        if (!viz2[s->inf])
        {
            k++;
            parc2(s->inf);
        } 
        s=s->leg;
    }
    fout<<k<<"\n";
    for(i=1; i<=k; i++)
       afisare(c[i]);
 
    return 0;
}