#include <bits/stdc++.h>
using namespace std;
#define NMAX 100009

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

  private:
    vector<int> adj[NMAX];
    vector<int> found;
    vector<int> low_link;
    vector<int> in_stack;
    vector<vector<int>> ctc;
    stack<int> st;
    int n, m;

    void read_input() {
        ifstream fin("ctc.in");
        fin >> n >> m;

        found = vector<int>(n + 1, -1);
        low_link = vector<int>(n + 1, 0);
        in_stack = vector<int>(n + 1, 0);

        for (int i = 1; i <= m; ++i) {
            int x, y;
            fin >> x >> y;

            adj[x].push_back(y);
        // adj[y].push_back(x);
        }
        fin.close();
    }

    void get_result() {
        int current_start = 0;
        
        for (int i = 1; i <= n; ++i) {
            if (found[i] == -1) {
                tarjan(i, current_start);
            }
        }
    }

    void tarjan(int node, int &current_start) {
        found[node] = current_start;
        low_link[node] = current_start;

        in_stack[node] = 1;
        st.push(node);

        ++current_start;

        for (int neighbour : adj[node]) {
            if (found[neighbour] == -1) {
                tarjan(neighbour, current_start);
                low_link[node] = min(low_link[node], low_link[neighbour]);
            } else {
                if (in_stack[neighbour] == 1) {
                    low_link[node] = min(low_link[node], found[neighbour]);
                }
            }
        }

        if (low_link[node] == found[node]) {
            int current;
            vector<int> new_ctc;

            while (!st.empty() && current != node) {
                current = st.top();
                st.pop();
                new_ctc.push_back(current);

                in_stack[current] = 0;
            }
            ctc.push_back(new_ctc);
        }
    }

    void print_output() {
        ofstream fout("ctc.out");
        fout << ctc.size() << "\n";
        for (vector<int> comp : ctc) {
            for (int el : comp) {
                fout << el << " ";
            }
            fout << "\n";
        }
        fout.close();
    }
};

int main() {
    Task *task = new Task();
    task->solve();
    delete task;

    return 0;
}