#include <fstream>
#include <vector>
#include <stdio.h>
#define NM 100005
using namespace std;
/*ifstream hai("ctc.in");
ofstream pa("ctc.out");*/

FILE *hai=fopen("ctc.in","r");
FILE *pa=fopen("ctc.out","w");

vector<int> G[NM],GT[NM],CTC[NM];

int n, m, viz[NM], st[NM], t = 0, k = 0;

void Dfs(int x);
void Dfst(int x);

int main(){
  int x,y,i,j;
  //hai >> n >> m;
  fscanf(hai,"%d %d", &n,&m);
  while(m){
    //hai >> x >> y;
    fscanf(hai,"%d %d",&x,&y);
    G[x].push_back(y);
    GT[y].push_back(x);
    m--;
  }
  for(i = 1; i <= n; i++)
    if(!viz[i])
      Dfs(i);
  // free the viz
  for(i = 1; i <= n; i++)
    viz[i] = 0;
  for(i = n; i >= 1; i--)
    if(!viz[st[i]]){
      k++;
      Dfst(st[i]);
    }
  //pa << k << endl;
  fprintf(pa,"%d\n",k);
  for(i = 1; i <= k; i++){
    for(j = 0; j < CTC[i].size();j++)
      //pa << CTC[i][j] << " ";
      fprintf(pa,"%d ",CTC[i][j]);
    //pa << endl;
    fprintf(pa,"\n");
  }
}

void Dfs(int x){
  int i, w;
  viz[x] = 1;
  for(i = 0; i < G[x].size(); i++){
    w = G[x][i];
    if(!viz[w])
      Dfs(w);
  }
  t++;
  st[t] = x;
}

void Dfst(int x){
  int w;
  viz[x] = 1;
  CTC[k].push_back(x);
  for(int i = 0; i < GT[x].size();i++){
    w = GT[x][i];
    if(!viz[w])
      Dfst(w);
  }
}