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

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

int n, m, st[100005], nctc;
bool viz_g[100005], viz_gt[100005];
vector<int> g[100005];
vector<int> gt[100005]; // graful transpus
vector<int> ctc[100005];

void citire();
void dfs_g(int x);
void dfs_gt(int x);

int main() {
    citire();

    // "Sortare topologica"
    for (int i = 1; i <= n; ++i) {
        if (!viz_g[i]) dfs_g(i);
    }

    // DFS pe graful transpus in ordine topologica
    for (int i = n; i >= 1; --i) {
        if (!viz_gt[st[i]]) {
            nctc++;
            dfs_gt(st[i]);
        }
    }

    out << nctc << '\n';
    for (int i = 1; i <= nctc; ++i) {
        for (int j = 0; j < ctc[i].size(); ++j)
            out << ctc[i][j] << " ";
        out << '\n';
    }

    return 0;
}


void dfs_gt(int x) {
    viz_gt[x] = true;
    for (int i = 0; i < gt[x].size(); ++i) {
        int y = gt[x][i];
        if (!viz_gt[y]) dfs_gt(y);
    }

    ctc[nctc].push_back(x);
}

void dfs_g(int x) {
    viz_g[x] = true;
    for (int i = 0; i < g[x].size(); ++i) {
        int y = g[x][i];
        if (!viz_g[y]) dfs_g(y);
    }

    st[++st[0]] = x;
}

void citire() {
    in >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int x, y;
        in >> x >> y;
        g[x].push_back(y);
        gt[y].push_back(x);
    }
}