#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <queue>
#define MAXN 100005
using namespace std;

vector <int> graf[MAXN];
vector <int> ginv[MAXN];
vector <int> ans[MAXN];
vector <int> parc;
int seen[MAXN];

void DFS(int node){
  seen[node]=1;
  for(int neigh : graf[node]){
    if(seen[neigh]==0){
      DFS(neigh);
    }
  }
  parc.push_back(node);
}

void DFS2(int node,int poz){
  seen[node]=1;
  for(int neigh : ginv[node]){
    if(seen[neigh]==0){
      DFS2(neigh,poz);
    }
  }
  ans[poz].push_back(node);
}

int main(){
  int n,m,i,x,y,k;
  FILE *fin,*fout;
  fin=fopen("ctc.in","r");
  fout=fopen("ctc.out","w");
  fscanf(fin,"%d%d",&n,&m);

  for(i=0;i<m;i++){
    fscanf(fin,"%d%d",&x,&y);
    graf[x].push_back(y);
    ginv[y].push_back(x);
  }

  for(i=1;i<=n;i++){
    if(seen[i]==0){
      DFS(i);
    }
  }

  for(i=1;i<=n;i++){
    seen[i]=0;
  }

  k=0;
  while(!parc.empty()){
    int node=parc.back();
    parc.pop_back();
    if(seen[node]==0){
      DFS2(node,k);
      k++;
    }
  }

  fprintf(fout,"%d\n",k);
  for(i=0;i<k;i++){
    for(int node : ans[i]){
      fprintf(fout,"%d ",node);
    }
    fprintf(fout,"\n");
  }

  fclose(fin);
  fclose(fout);
  return 0;
}