#include <fstream>
#include <algorithm>
#include <vector>

using namespace std;

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

#define MAXN 100000

int vf, k, q, st[MAXN + 1], viz[MAXN + 1], best[MAXN + 1];
bool ok[MAXN + 1];
vector <int> g[MAXN + 1], c[MAXN + 1];

void dfs(int x) {
    st[++vf] = x;
    viz[x] = best[x] = ++k;
    ok[x] = 1;
    for (auto &y : g[x]) {
        if (viz[y] == 0) {
            dfs(y);
            best[x] = min(best[x], best[y]);
        } else if (ok[y]) best[x] = min(best[x], viz[y]);
    }
    if (viz[x] == best[x]) {
        while (st[vf] != x) {
            c[q].push_back(st[vf]);
            ok[st[vf]] = 0;
            vf--;
        }
        c[q++].push_back(x);
        ok[x] = 0;
        vf--;
    }
}

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

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

        g[x].push_back(y);
    }

    for (int i = 1; i <= n; i++)
        if (viz[i] == 0)
            dfs(i);

    fout << q << '\n';
    for (int i = 0; i < q; i++) {
        for (auto &x : c[i])
            fout << x << ' ';
        fout << '\n';
    }

    return 0;
}