#include <fstream>
#include <vector>

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

const int MAXN = 100005;

int n, m;
vector<int> adj[MAXN];

int idx[MAXN];
int low[MAXN];
bool inStiva[MAXN];
vector<int> stiva;
int timer;

vector<vector<int>> componente;

void dfsTarjan(int u) {
    timer++;
    idx[u] = timer;
    low[u] = timer;

    stiva.push_back(u);
    inStiva[u] = true;

    for (int i = 0; i < adj[u].size(); i++) {
        int v = adj[u][i];

        if (idx[v] == 0) {
            dfsTarjan(v);

            if (low[v] < low[u]) {
                low[u] = low[v];
            }
        } else {
            if (inStiva[v] == true) {
                if (idx[v] < low[u]) {
                    low[u] = idx[v];
                }
            }
        }
    }

    if (idx[u] == low[u]) {
        vector<int> componentaCurenta;

        while (true) {
            int v = stiva.back();
            stiva.pop_back();
            inStiva[v] = false;

            componentaCurenta.push_back(v);

            if (u == v) {
                break;
            }
        }

        componente.push_back(componentaCurenta);
    }
}

int main() {
    fin >> n >> m;

    for (int i = 1; i <= m; i++) {
        int x, y;
        fin >> x >> y;
        adj[x].push_back(y);
    }

    for (int i = 1; i <= n; i++) {
        if (idx[i] == 0) {
            dfsTarjan(i);
        }
    }

    fout << componente.size() << "\n";

    for (int i = 0; i < componente.size(); i++) {
        for (int j = 0; j < componente[i].size(); j++) {
            fout << componente[i][j] << " ";
        }
        fout << "\n";
    }

    fin.close();
    fout.close();

    return 0;
}