#include <iostream>
#include <map>
#include <vector>
#include <fstream>
using namespace std;

ifstream f("ctc.in");
ofstream g("ctc.out");

int n, m;
int n_dfs_forest;
int n_scc;

vector <int> * lvg;
vector <int> * lvgt;

vector <vector <int>> dfs_forest;
int * visited;  /// visited[i] =  | (value of initial dfs tree root), after first DFS
                ///               | -1 , after being found to be part of a SCC

vector <vector<int>> scc;

void DFS(int node){

    for (int i = 0; i < lvg[node].size(); i++)

        if (!visited[lvg[node][i]]){

            visited[lvg[node][i]] = visited[node];
            DFS(lvg[node][i]);
        }

    dfs_forest[n_dfs_forest - 1].push_back(node);
}

void DFS_transposed(int node){

    scc[n_scc - 1].push_back(node);

    for (int i = 0; i < lvgt[node].size(); i++){

        if (visited[lvgt[node][i]] > 0){

            visited[lvgt[node][i]] = -1;
            DFS_transposed(lvgt[node][i]);
        }
    }
}


int main(){

    f >> n >> m;

    lvg = new vector <int> [n + 1];
    lvgt = new vector <int> [n + 1];

    visited = new int[n + 1];

    for(int i = 0; i <= n; i++){

        visited[i] = 0;
    }

    int x, y;
    for (int cnt = 0; cnt < m; cnt++){

        f >> x >> y;

        lvg[x].push_back(y);
        lvgt[y].push_back(x);
    }

    /*for (int i = 1; i <= n; i++){

        g << i << ": ";

        for (int j = 0; j < lvg[i].size(); j++)
            g << lvg[i][j] << " ";

        g << '\n';
    }

    for (int i = 1; i <= n; i++){

        g << i << ": ";

        for (int j = 0; j < lvgt[i].size(); j++)
            g << lvgt[i][j] << " ";

        g << '\n';
    }*/

    for (int i = 1; i <= n; i++){

        if (!visited[i]){

            n_dfs_forest = dfs_forest.size() + 1;
            dfs_forest.resize(n_dfs_forest);

            visited[i] = i;
            DFS(i);

            while (dfs_forest[n_dfs_forest - 1].size() > 0){

                int current_node = dfs_forest[n_dfs_forest - 1].back();
                dfs_forest[n_dfs_forest - 1].pop_back();

                if (visited[current_node] > 0){

                    n_scc = scc.size() + 1;
                    scc.resize(n_scc);

                    visited[current_node] = -1;
                    DFS_transposed(current_node);
                }
            }
        }
    }

    g << scc.size() << '\n';
    for (int i = 0; i < scc.size(); i++){

        for (int j = 0; j < scc[i].size(); j++){

            g << scc[i][j] << " ";
        }
        g << '\n';
    }

    /*for (int i = 0; i < dfs_forest.size(); i++){

        for (int j = 0; j < dfs_forest[i].size(); j++){

            g << dfs_forest[i][j] << " ";
        }

        g << '\n';
    }*/

    return 0;
}