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

class Task {
public:
    void solve() {
        read_input();
        get_result();
        print_output();
    }

private:
    static constexpr int NMAX = (int)1e5 + 5;

    int n, m, components;

    vector<int> adj[NMAX];
    vector<int> new_scc[NMAX];
    vector<int> stk;

    void read_input() {
        ifstream fin("ctc.in");
        fin >> n >> m;
        for (int i = 1, x, y; i <= m; i++) {
            fin >> x >> y;
            adj[x].push_back(y);
        }
        fin.close();
    }

    void DFS(int node, vector<int> &p, int &timestamp, vector<int>& found,
             vector<int>& low_link, vector<int>& visited) {
        found[node] = ++timestamp;
        low_link[node] = found[node];
        stk.push_back(node);
        visited[node] = 1;

        for (int neigh : adj[node]) {
            if (p[neigh] != -1) {
                if (visited[neigh] == 1) {
                    low_link[node] = min(low_link[node], found[neigh]);
                }
                continue;
            }
            p[neigh] = node;

            DFS(neigh, p, timestamp, found, low_link, visited);
            
            low_link[node] = min(low_link[node], low_link[neigh]);
        }

        if (low_link[node] == found[node]) {
            int x;

            do {
                x = stk.back();
                stk.pop_back();
                visited[x] = 0;
                new_scc[components].push_back(x);
            } while (x != node);
            components++;
        }
    }

    void get_result() {
        vector<int> found(n + 1);
        vector<int> p (n + 1);
        vector<int> low_link(n + 1);
        vector<int> visited(n + 1);
        components = 0;

        for (int i = 1; i <= n; i++) {
            p[i] = -1;
            found[i] = NMAX;
            low_link[i] = NMAX;
        }
        int timestamp = 0;

        for (int i = 1; i <= n; i++) {
            if (p[i] == -1) {
                p[i] = i;
                DFS(i, p, timestamp, found, low_link, visited);
            }
        }
    }

    void print_output() {
        ofstream fout("ctc.out");
        fout << components << endl;
        for (int i = 0; i <= components; i++) {
            for (int j = 0; j < new_scc[i].size(); j++) {
                fout << new_scc[i][j] << " ";
            }
            fout << endl;
        }
        fout.close();
    }
};

int main() {
    auto* task = new (nothrow) Task();
    if (!task) {
        cerr << "new failed: WTF are you doing? Throw your PC!\n";
        return -1;
    }
    task->solve();
    delete task;
    return 0;
}