#include<cstdio>
#include<vector>
#include<stack>
const int NMAX=100010;
std::vector<int> vecini[NMAX],multime;
std::vector<int> inv_vecini[NMAX];
std::stack<int> stiva;
bool viz[NMAX];
void componente(int nod)
{
 viz[nod]=true;
 bool pp=false;
 for(std::vector<int>::iterator it=vecini[nod].begin();it!=vecini[nod].end();it++)
     {
      if(!viz[*it])
         {
          pp=true;
          componente((*it));
         }
     }
 stiva.push(nod);
}
void inversare(int n)
{
 for(int i=1;i<=n;i++)
     {
      for(std::vector<int>::iterator it=vecini[i].begin();it!=vecini[i].end();it++)
          {
           inv_vecini[*it].push_back(i);
          }
     }
}
void verificare(int nod,int _multime)
{
 multime[nod]=_multime;
 for(std::vector<int>::iterator it=inv_vecini[nod].begin();it!=inv_vecini[nod].end();it++)
     {
      if(multime[*it]==0)
         {
          verificare((*it),_multime);
         }
     }
}
int main()
{
 FILE *in=fopen("ctc.in","r");
 int n,m;
 fscanf(in,"%d %d ",&n,&m);
 multime.resize(n+1);
 for(int i=1;i<=m;i++)
     {
      int x,y;
      fscanf(in,"%d %d ",&x,&y);
      vecini[x].push_back(y);
     }
 fclose(in);
 for(int i=1;i<=n;i++)
     if(!viz[i])
        componente(i);
 inversare(n);
 FILE *out=fopen("ctc.out","w");
 int _multime=1;
 for(int i=1;i<=n;i++)
     {
      if(multime[stiva.top()]==0)
         {
          verificare(stiva.top(),_multime++);
         }
      stiva.pop();
     }
 fprintf(out,"%d\n",_multime-1);
 for(int i=1;i<=_multime-1;i++)
     {
      for(int j=1;j<=n;j++)
          if(multime[j]==i)
             fprintf(out,"%d ",j);
      fprintf(out,"\n");
     }
 fclose(out);
 return 0;
}