#include <fstream>
#include <vector>
#define NMAX 100002

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

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

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

int main()
{int i;
  citire();
  ///etapa I
  for (i=1; i<=n; i++)
      if (!uz[i]) DFS(i);
  ///etapa II
  for (i=n; i>0; i--)
      if (!ctc[postordine[i]])
          {nrc++; DFST(postordine[i]);}
  afisare();
  return 0;
}

void citire()
{int i, x, y, m;
 fin>>n>>m;
 for (i=0; i<m; i++)
      {//arc
       fin>>x>>y;
       G[x].push_back(y);
       ///in graful transpus pun arcul (y,x)
       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;
 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=1; j<=n; j++)
          if (ctc[j]==i) fout<<j<<' ';
       fout<<'\n';
      }
}