#include <fstream>
#include <vector>

using namespace std;

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

int n, m, nrc, i = 1, j = 1;
vector<int> viz1;
vector<int> viz2;
vector<vector<int>> g;
vector<vector<int>> gt;
vector<int> comp;
vector<vector<int>> afis;

void dfs1(int nod) {
    viz1[nod] = 1;
    for (auto i : g[nod])
        if (!viz1[i])
            dfs1(i);
}

void dfs2(int nod) {
    viz2[nod] = 1;
    if (viz1[nod] && viz2[nod]) {
        comp[nod] = nrc;
        afis[nrc].push_back(nod);
    }
    for (auto i : gt[nod])
        if (!viz2[i])
            dfs2(i);
}

int main() {
    cin.tie(0);
    cin.sync_with_stdio(false);
    cin >> n >> m;
    afis.resize(n + 1);
    g.resize(n + 1);
    gt.resize(n + 1);
    comp.resize(n + 1);
    viz1.resize(n + 1);
    viz2.resize(n + 1);

    while (m) {
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
        gt[b].push_back(a);
        --m;
    }

    while (i - 1 != n) {
        if (!comp[i]) {
            ++nrc;
            dfs1(i);
            dfs2(i);
            while (j - 1 != n) {
                viz1[j] = viz2[j] = 0;
                ++j;
            }
        }
        ++i;
        j = 0;
    }
    cout << nrc << '\n';
    for (int i = 1; i <= nrc; ++i) {
        for (auto j : afis[i])
            cout << j << ' ';
        cout << '\n';
    }

    return 0;
}