// https://infoarena.ro/problema/ctc
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'

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

const int MAXN=100005;
bool viz[MAXN];
vector<int> component, order, adj[MAXN], rev[MAXN];

void dfs1(int x) {
  viz[x] = true;

  for (int y:adj[x]) {
    if (!viz[y]) dfs1(y);
  }
  order.push_back(x);
}

void dfs2(int x) {
  viz[x] = true;
  component.push_back(x);

  for (int y:rev[x]) {
    if (!viz[y]) dfs2(y);
  }
}

int main() {
  int n, m;
  fin>>n>>m;

  for (int i=0; i<m; ++i) {
    int x, y;
    fin>>x>>y;
    adj[x].push_back(y);
    rev[y].push_back(x);
  }

  for (int i=1; i<=n; ++i) {
    if (!viz[i]) dfs1(i);
  }
  reverse(order.begin(), order.end());

  for (int i=0; i<MAXN; ++i) viz[i] = false;

  vector<vector<int>> components{};
  for (int i=0; i<(int)order.size(); ++i) {
    if (!viz[order[i]]) {
      dfs2(order[i]);
      components.push_back(component);
      component.clear();
    }
  }

  fout<<components.size()<<endl;
  for (vector<int> comp:components) {
    for (int x:comp) fout<<x<<" ";
    fout<<endl;
  }
}