#include <fstream>
#include <vector>

using namespace std;

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

int n, m, nrc;
vector<int> viz1(100001);
vector<int> viz2(100001);
vector<vector<int>> g(100001);
vector<vector<int>> gt(100001);
vector<int> comp(100001);
vector<vector<int>> afis(100001);

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;
    for (int i = 1; i <= m; ++i) {
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
        gt[b].push_back(a);
    }

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

    return 0;
}