#pragma region header
#include <bits/stdc++.h>
// #define int long long
#define all(a) begin(a), end(a)
#define rall(a) rbegin(a), rend(a)
#define mp make_pair
#define rep1(i, n) for (decltype(+n) i = 0; i < (n); i++)
#define rrep1(i, n) for (auto i = n - 1; i > static_cast<decltype(i)>(-1); i--)
#define rep2(i, a, b) for (auto i = (a); i < (b); i++)
#define rrep2(i, a, b) for (auto i = b - 1; i >= a; i--)
#define GET_MACRO(_1, _2, _3, NAME, ...) NAME
#define rep(...) GET_MACRO(__VA_ARGS__, rep2, rep1) (__VA_ARGS__)
#define rrep(...) GET_MACRO(__VA_ARGS__, rrep2, rrep1) (__VA_ARGS__)
#define each(i, a) for (auto &&i : (a))
using namespace std;

using ld = long double;
using vi = vector<int>;
using vvi = vector<vi>;
using vs = vector<string>;
using vvs = vector<vs>;
using vd = vector<ld>;
using vvd = vector<vd>;
using vb = vector<bool>;
using vvb = vector<vb>;
using pii = pair<int, int>;
using vp = vector<pii>;
using vvp = vector<vp>;
using mii = map<int, int>;
using vm = vector<mii>;
using vvm = vector<vm>;
template <class T, class U>
using umap = unordered_map<T, U>;
using umii = umap<int, int>;
using seti = set<int>;
template <class T>
using uset = unordered_set<T>;
using useti = uset<int>;
template <class T>
using less_queue = priority_queue<T>;
template <class T>
using greater_queue = priority_queue<T, vector<T>, greater<T>>;
using int128 = __int128_t;

ostream &operator<<(ostream &dest, int128 value) {
  ostream::sentry s(dest);
  if (s) {
    int128 tmp = value < 0 ? -value : value;
    char buffer[128];
    char *d = end(buffer);
    do {
      --d;
      *d = "0123456789"[tmp % 10];
      tmp /= 10;
    } while (tmp != 0);
    if (value < 0) {
      --d;
      *d = '-';
    }
    int len = end(buffer) - d;
    if (dest.rdbuf()->sputn(d, len) != len) {
      dest.setstate(ios_base::badbit);
    }
  }
  return dest;
}

// const int INF = 1e18;
const ld EPS = 1e-10;

template <class T>
void SORT(T &a) { stable_sort(all(a)); }
template <class T>
void RSORT(T &a) { stable_sort(rall(a)); }
template <class T>
void rev(T &a) { reverse(all(a)); }
template <class T>
void uniq(T &a) { a.erase(unique(all(a)), end(a)); }
template <class T>
auto min_of(const T &a) { return *min_element(all(a)); }
template <class T>
auto max_of(const T &a) { return *max_element(all(a)); }
template <class T>
T sum_of(const vector<T> &a) { return accumulate(all(a), (T)0); }
template <class T, class U>
int count_of(const T &a, const U &i) { return count(all(a), i); }
template <class T>
bool has(const vector<T> &a, const T &i) { return find(all(a), i) != a.end(); }
bool has(const string &a, const char &i) { return find(all(a), i) != a.end(); }
template <class T>
bool has(const set<T> &a, const T &i) { return a.find(i) != a.end(); }
template <class T, class U>
bool has(const map<T, U> &a, const T &i) { return a.find(i) != a.end(); }
template <class T, class U>
bool has(const umap<T, U> &a, const T &i) { return a.find(i) != a.end(); }
template <class T>
int sz(const T &a) { return a.size(); };

template <class T>
void COUT(const T &x) { cout << x << '\n'; }
template <class T, class U>
void COUT(const T &x, const U &y) { cout << x << ' ' << y << '\n'; }
template <class T, class U, class V>
void COUT(const T &x, const U &y, const V &z) { cout << x << ' ' << y << ' ' << z << '\n'; }
template <class T>
void CSP(const T &x) { cout << x << ' '; }
template <class T>
void CVEC(const T &v) {
  int c = v.size() - 1;
  for (int i = 0; i < c; i++) cout << v[i] << ' ';
  if (c > -1) cout << v[c];
  cout << '\n';
}

template <class T>
bool amin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
bool amax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

constexpr int lshift(const int &x) noexcept { return 1ll << x; }
constexpr int popcount(const unsigned int &x) noexcept { return __builtin_popcountll(x); }
constexpr int least1(const unsigned int &x) noexcept { return __builtin_ffsll(x); }
constexpr int ceil_div(const int &x, const int &y) noexcept { return (x + y - 1) / y; }

#pragma endregion header

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);
  }

  vvi scc() { return internal.scc(); }

private:
  template <class E>
  struct csr {
    vi start;
    vector<E> elist;
    csr(int n, const vector<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;
    }
  };

  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}}); }

    pair<int, vi> scc_ids() {
      auto g = csr<edge>(_n, edges);
      int now_ord = 0, group_num = 0;
      vi 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] = min(low[v], low[to]);
          } else {
            low[v] = 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};
    }

    vvi scc() {
      auto ids = scc_ids();
      int group_num = ids.first;
      vi counts(group_num);
      for (auto x : ids.second) counts[x]++;
      vvi 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; };
    vector<pair<int, edge>> edges;
  };

  _scc_graph internal;
};

#pragma region main
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(15);

  int N, M;
  cin >> N >> M;
  scc_graph g(N);
  rep(i, M) {
    int a, b;
    cin >> a >> b;
    g.add_edge(a, b);
  }
  vvi ans = g.scc();
  COUT(sz(ans));
  each(x, ans) {
    CSP(sz(x));
    CVEC(x);
  }
}
#pragma endregion main

Measured memory_bytes: 40124