#include <iostream>
#include <cstdio>
using namespace std;
   
 
   
struct Nod{int inf; Nod* leg;};
typedef Nod* nod;
   
nod a[100001],b[100001],s,c[100001];
   
int n,m,k;
bool viz[100001],viz2[100001];
void afisare(nod q)
{
    if(q){cout<<q->inf<<" "; afisare(q->leg);}
    else cout<<endl;
}
   
/*void adaug(nod &q, int x)
{
    nod p=new Nod;
    p->inf=x;
    p->leg=q;
    q=p;
}*/
void adaug(int x, int y)
{
    nod p=new Nod;
    p->inf=y;
    p->leg=a[x];
    a[x]=p;
}

void adaug2(int x, int y)
{
    nod p=new Nod;
    p->inf=y;
    p->leg=b[x];
    b[x]=p;
}

void adaug3(int x)
{
    nod p=new Nod;
    p->inf=x;
    p->leg=s;
    s=p;
}
void adaug4(int x, int y)
{
    nod p=new Nod;
    p->inf=y;
    p->leg=c[x];
    c[x]=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);
	adaug3(i);
}
   
void parc2(int i)
{
    viz2[i]=1;//
    //adaug(c[k],i);
	adaug4(k,i);
    for(nod j=b[i]; j; j=j->leg) if (!viz2[j->inf]) parc2(j->inf);//
}
   
int main()
{
    freopen ("ctc.in","r",stdin);
    freopen ("ctc.out","w",stdout);
    int i,x,y;
    cin>>n>>m;
    for(i=1; i<=m; i++)
    {
        cin>>x>>y;
        //adaug(a[x],y);
        //adaug(b[y],x);
		adaug(x,y);
		adaug2(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;
    }
    cout<<k<<"\n";
    for(i=1; i<=k; i++)
       afisare(c[i]);
  
    return 0;
}