#include <bits/stdc++.h>

using namespace std;

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

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

    int n, m, source, timestamp = 0;
    vector<int> adj[NMAX];

    vector<int> parent;
    vector<int> found;
    vector<int> low_link;
    stack<int> nodes_stack;
    vector<bool> in_stack;

    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();
    }

    // TARJAN
    vector<vector<int>> ctc_tarjan() {
        vector<vector<int>> ctc;
        parent.resize(n + 1, -1);
        found.resize(n + 1, 0);
        low_link.resize(n + 1, 0);
        in_stack.resize(n + 1, false);

        for (int node = 1; node <= n; ++node) {
            if (parent[node] == -1) {
                parent[node] = node;
                dfs(node, ctc);
            }
        }

        return ctc;
    }

    void dfs(int node, vector<vector<int>> &ctc) {
        found[node] = ++timestamp;
        low_link[node] = timestamp;
        nodes_stack.push(node);
        in_stack[node] = true;

        for (auto &neighbor : adj[node]) {
            if (parent[neighbor] == -1) {
                parent[neighbor] = node;
                dfs(neighbor, ctc);
                low_link[node] = min(low_link[node], low_link[neighbor]);
            } else if (in_stack[neighbor]) {
                low_link[node] = min(low_link[node], found[neighbor]);
            }
        }

        if (found[node] == low_link[node]) {
            vector<int> scc;
            int x;
            do {
                x = nodes_stack.top();
                nodes_stack.pop();
                in_stack[x] = false;
                scc.push_back(x);
            } while (x != node);
            ctc.push_back(scc);
        }
    }

    void print_output(const vector<vector<int>> &ctc) {
        ofstream fout("ctc.out");
        fout << ctc.size() << '\n';
        for (const auto &scc : ctc) {
            for (auto node : scc) {
                fout << node << ' ';
            }
            fout << '\n';
        }
        fout.close();
    }
};

int main() {
    auto* task = new (nothrow) Task();
    if (!task) {
        cerr << "Error\n";
        return -1;
    }
    task->solve();
    delete task;
    return 0;
}