#line 1 "/workspaces/compro/lib/atcoder/scc.hpp"



#line 1 "/workspaces/compro/lib/atcoder/internal_scc.hpp"



#include <algorithm>
#include <utility>
#include <vector>

namespace atcoder {
namespace internal {

template <class E> struct csr {
    std::vector<int> start;
    std::vector<E> elist;
    csr(int n, const std::vector<std::pair<int, E>>& edges)
        : start(n + 1), elist(edges.size()) {
        for (auto e : edges) {
            start[e.first + 1]++;
        }
        for (int i = 1; i <= n; i++) {
            start[i] += start[i - 1];
        }
        auto counter = start;
        for (auto e : edges) {
            elist[counter[e.first]++] = e.second;
        }
    }
};

// Reference:
// R. Tarjan,
// Depth-First Search and Linear Graph Algorithms
struct scc_graph {
  public:
    scc_graph(int n) : _n(n) {}

    int num_vertices() { return _n; }

    void add_edge(int from, int to) { edges.push_back({from, {to}}); }

    // @return pair of (# of scc, scc id)
    std::pair<int, std::vector<int>> scc_ids() {
        auto g = csr<edge>(_n, edges);
        int now_ord = 0, group_num = 0;
        std::vector<int> visited, low(_n), ord(_n, -1), ids(_n);
        visited.reserve(_n);
        auto dfs = [&](auto self, int v) -> void {
            low[v] = ord[v] = now_ord++;
            visited.push_back(v);
            for (int i = g.start[v]; i < g.start[v + 1]; i++) {
                auto to = g.elist[i].to;
                if (ord[to] == -1) {
                    self(self, to);
                    low[v] = std::min(low[v], low[to]);
                } else {
                    low[v] = std::min(low[v], ord[to]);
                }
            }
            if (low[v] == ord[v]) {
                while (true) {
                    int u = visited.back();
                    visited.pop_back();
                    ord[u] = _n;
                    ids[u] = group_num;
                    if (u == v) break;
                }
                group_num++;
            }
        };
        for (int i = 0; i < _n; i++) {
            if (ord[i] == -1) dfs(dfs, i);
        }
        for (auto& x : ids) {
            x = group_num - 1 - x;
        }
        return {group_num, ids};
    }

    std::vector<std::vector<int>> scc() {
        auto ids = scc_ids();
        int group_num = ids.first;
        std::vector<int> counts(group_num);
        for (auto x : ids.second) counts[x]++;
        std::vector<std::vector<int>> groups(ids.first);
        for (int i = 0; i < group_num; i++) {
            groups[i].reserve(counts[i]);
        }
        for (int i = 0; i < _n; i++) {
            groups[ids.second[i]].push_back(i);
        }
        return groups;
    }

  private:
    int _n;
    struct edge {
        int to;
    };
    std::vector<std::pair<int, edge>> edges;
};

}  // namespace internal

}  // namespace atcoder


#line 6 "/workspaces/compro/lib/atcoder/scc.hpp"
#include <cassert>
#line 8 "/workspaces/compro/lib/atcoder/scc.hpp"

namespace atcoder {

struct scc_graph {
public:
  scc_graph() : internal(0) {}
  scc_graph(int n) : internal(n) {}

  void add_edge(int from, int to) {
    int n = internal.num_vertices();
    assert(0 <= from && from < n);
    assert(0 <= to && to < n);
    internal.add_edge(from, to);
  }

  std::vector<std::vector<int>> scc() { return internal.scc(); }

private:
  internal::scc_graph internal;
};

} // namespace atcoder


#line 1 "/workspaces/compro/lib/template.hpp"


#line 1 "/workspaces/compro/lib/io/vector.hpp"
#include <iostream>
#line 3 "/workspaces/compro/lib/io/vector.hpp"

#ifndef IO_VECTOR
#define IO_VECTOR

template <class T> std::ostream &operator<<(std::ostream &out, const std::vector<T> &v) {
  int size = v.size();
  for (int i = 0; i < size; i++) {
    std::cout << v[i];
    if (i != size - 1)
      std::cout << " ";
  }
  return out;
}

template <class T> std::istream &operator>>(std::istream &in, std::vector<T> &v) {
  for (auto &el : v) {
    std::cin >> el;
  }
  return in;
}

#endif
#line 4 "/workspaces/compro/lib/template.hpp"
#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define ALL(v) (v).begin(), (v).end()
#define coutd(n) cout << fixed << setprecision(n)
#define ll long long int
#define vl vector<ll>
#define vi vector<int>
#define MM << " " <<

using namespace std;

template <class T> void say(bool val, T yes, T no) { cout << (val ? yes : no) << "\n"; }

void say(bool val, string yes = "Yes", string no = "No") { say<string>(val, yes, no); }

template <class T> void chmin(T &a, T b) {
  if (a > b)
    a = b;
}

template <class T> void chmax(T &a, T b) {
  if (a < b)
    a = b;
}

// C++ 17に完全移行したら消す
// 最大公約数を求める
template <class T> T gcd(T n, T m) { return n ? gcd(m % n, n) : m; }

// 最小公倍数を求める
template <class T> T lcm(T n, T m) {
  int g = gcd(n, m);
  return n * m / g;
}

// 重複を消す。計算量はO(NlogN)
template <class T> void unique(std::vector<T> &v) {
  std::sort(v.begin(), v.end());
  v.erase(std::unique(v.begin(), v.end()), v.end());
}


#line 3 "main.cpp"

// generated by online-judge-template-generator v4.4.0 (https://github.com/kmyk/online-judge-template-generator)
int main() {
  int N;
  int M;
  std::cin >> N >> M;

  atcoder::scc_graph g(N);

  REP(i, M) {
    int a, b;
    cin >> a >> b;
    g.add_edge(a, b);
  }

  auto scc = g.scc();

  cout << scc.size() << "\n";
  for (const auto v : scc) {
    cout << v.size() << " " << v << endl;
  }
}


Measured memory_bytes: 40100