#include <fstream>
#include <vector>
#define NMAX 100005

using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");

int n,m,nr,nrc;
vector <int> G[NMAX];
vector <int> GT[NMAX];
vector <int> CTC[NMAX];
int postordine[NMAX];
bool uz[NMAX];
int ctc[NMAX];
///ctc[i]=componenta tare conexa din care face parte vf i

void citire();
void DFS(int x);
void DFST(int x);
void afisare();

int main()
{
 int i;
 citire();
 ///etapa 1
 for (i=1;i<=n;i++)
     if (!uz[i]) DFS(i);
 ///etapa 2
for (i=n;i>0;i--)
    if (!ctc[postordine[i]])
       {
        nrc++;
        DFST(postordine[i]);
       }
 afisare();
 return 0;
}
void citire()
{
 int i,x,y;
 fin>>n>>m;
 for (i=0;i<m;i++)
     {
      fin>>x>>y;
      G[x].push_back(y);
      GT[y].push_back(x);
     }
}
void DFS(int x)
{
 int i;
 uz[x]=1;
 for (i=0;i<G[x].size();i++)
      if (uz[G[x][i]]==0)
          DFS(G[x][i]);
 nr++;
 postordine[nr]=x;
}
void DFST(int x)
{
 int i;
 ctc[x]=nrc;
 CTC[nrc].push_back(x);
 for (i=0;i<GT[x].size();i++)
      if (ctc[GT[x][i]]==0)
          DFST(GT[x][i]);
}
void afisare()
{
 int i,j;
 fout<<nrc<<'\n';
 for (i=1;i<=nrc;i++)
     {
      for (j=0;j<CTC[i].size();j++)
          fout<<CTC[i][j]<<' ';
      fout<<'\n';
     }
}