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

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

private:
    // numarul maxim de noduri
    static constexpr int NMAX = (int)1e5 + 5; // 10^5 + 5 = 100.005

    // n = numar de noduri, m = numar de muchii/arce
    int n, m;

    // adj[node] = lista de adiacenta a nodului node
    // exemplu: daca adj[node] = {..., neigh, ...} => exista arcul (node, neigh)
    vector<int> adj[NMAX];

    // parent[node] = parent of node in the DFS traversal
    vector<int> parent;

    // found[node] = the timestamp when we found node (we started to visit its subtree)
    // Note: The global timestamp is incremented everytime we find a node.
    vector<int> found;

    // low_link[node] = min { found[x] | x can be accesed from node }
    //                = the minimum timestamp that node can see (directly or indirectly through its descendents)
    vector<int> low_link;

    // nodes are pushed into the stack in the order of visiting
    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); // arc (x, y)
        }
        fin.close();
    }

    vector<vector<int>> get_result() {
        // TODO: Gasiti componentele tare conexe ale grafului orientat cu n noduri, stocat in adj.
        // Rezultatul se va returna sub forma unui vector, ale carui elemente sunt componentele tare conexe detectate.
        // Nodurile si componentele tare conexe pot fi puse in orice ordine in vector.
        //

        return tarjan_scc();
    }

    vector<vector<int>> tarjan_scc() {
        // STEP 0: initialize results
        parent = vector<int>(n + 1, -1);
        found = vector<int>(n + 1, -1);
        low_link = vector<int>(n + 1, -1);
        in_stack = vector<bool>(n + 1, false);

        // STEP 2: visit all nodes for computing all SCCs
        vector<vector<int>> all_sccs;
        int timestamp = 0;                                         // global timestamp
        for (int node = 1; node <= n; ++node) {
            if (parent[node] == -1) {                              // node not visited
                parent[node] = node;                               // convention: the parent of the root is actually the root
                cout << node << '\n';
                dfs(node, timestamp, all_sccs);                    // start a new DFS traversal for substree with root in node
            }
        }

        return all_sccs;
    }

    void dfs(int node, int &timestamp, vector<vector<int>>& all_sccs) {
        // STEP 1: a new node is visited - increment the timestamp
        found[node]    = ++timestamp;                              // the timestamp when node was found
        low_link[node] = found[node];                              // node only knows its timestamp
        nodes_stack.push(node);
        in_stack[node] = true;

        // STEP 2: visit each neighbour
        int children = 0;                                          // the number of found children
        for (auto neigh : adj[node]) {
            // STEP 3: check if neigh is already visited
            if (parent[neigh] != -1) {
                // STEP 3.1: neigh already visited - update low_link[node] with information gained through neigh
                if (/*neigh != parent[node] && */in_stack[neigh]) {                       //
                    low_link[node] = min(low_link[node], found[neigh]);
                }
                continue;
            }

            // STEP 4: save parent and could children
            parent[neigh] = node;
            ++children;

            // STEP 5: recursively visit the child subree
            dfs(neigh, timestamp, all_sccs);

            // STEP 6: update low_link[node] with information gained through neigh
            low_link[node] = min(low_link[node], low_link[neigh]);
        }

        // STEP 8: check for SCCs: node is root in a SCC if low_link[node] == found[node]
        if (low_link[node] == found[node]) {
            // STEP 8.1: extract current SCC - pop nodes from stack until node is found
            vector<int> scc;
            do {
                auto x = nodes_stack.top();
                nodes_stack.pop();
                in_stack[x] = false;

                scc.push_back(x);
            } while(scc.back() != node);

            // STEP 8.2: save SCC
            all_sccs.push_back(scc);
        }
    }

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

// [ATENTIE] NU modifica functia main!
int main() {
    // * se aloca un obiect Task pe heap
    // (se presupune ca e prea mare pentru a fi alocat pe stiva)
    // * se apeleaza metoda solve()
    // (citire, rezolvare, printare)
    // * se distruge obiectul si se elibereaza memoria
    auto* task = new (nothrow) Task(); // hint: cppreference/nothrow
    if (!task) {
        cerr << "new failed: WTF are you doing? Throw your PC!\n";
        return -1;
    }
    task->solve();
    delete task;
    return 0;
}