#include <bits/stdc++.h>
using namespace std;

        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;
                }
            }
        };
 
        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;
        };

int main(){
    int n, m; cin >> n >> m;
    scc_graph data(n);
    for (int i = 0; i < m; i++) {
        int a, b; cin >> a >> b;
        data.add_edge(a, b);
    }
    auto ans = data.scc();
    cout << (int)ans.size() << "\n";
    for (auto p : ans) {
        cout << (int)p.size() << " ";
        for (auto pp : p) cout << pp << " ";
        cout << "\n";
    }
    return 0;
}

Measured memory_bytes: 40584