#include<fstream>
#include<vector>

using namespace std;

vector<int> st, st2, graph[100005], gt[100005];
vector<vector<int> > ctc;
int vis[100005], vis2[100005];

void dfs1(int x){
  vis[x] = 1;
  st.push_back(x);
  for(int i = 0; i < graph[x].size(); ++i)
    if(!vis[graph[x][i]])
      dfs1(graph[x][i]);
}

void dfs2(int x){
  vis2[x] = 1;
  st2.push_back(x);
  for(int i = 0; i < gt[x].size(); ++i)
    if(!vis2[gt[x][i]])
      dfs2(gt[x][i]);
}

int main(){
  ifstream in("ctc.in");
  ofstream out("ctc.out");

  int n, m;
  in >> n >> m;

  for(int i = 1; i <= m; ++i){
    int x, y;
    in >> x >> y;
    graph[x].push_back(y);
    gt[y].push_back(x);
  }

  for(int i = 1; i <= n; ++i)
    if(!vis[i])
      dfs1(i);

  for(int i = n - 1; i >= 0; --i)
    if(!vis2[st[i]]){
      dfs2(st[i]);
      ctc.push_back(st2);
      st2.clear();
    }

  out << ctc.size() << "\n";
  for(int i = 0; i < ctc.size(); ++i){
    for(int j = 0; j < ctc[i].size(); ++j)
      out << ctc[i][j] << " ";
    out << "\n";
  }

  return 0;
}