#include <fstream>
#include <vector>
#include <set>

using namespace std;

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

const int Nmax = 1e6;
int cnt = 0;
vector<int> g[Nmax], gt[Nmax];
vector<int> topo, use, ctc(Nmax);
set<int> group[Nmax];

void dfs(int nod) {
    use[nod] = 1;
    for (int i : g[nod])
        if (!use[i])
            dfs(i);

    topo.push_back(nod);
}

void dfst (int nod, int idx) {
    use[nod] = 1;
    for (int i : g[nod])
        if (!use[i])
            dfst(i, idx);

    group[idx].insert(nod);
}

int main()
{
    int n,m;
    cin >> n >> m;
    for (int i = 0; i < m; i++)
    {
        int x,y;
        cin >> x >> y;
        g[x].push_back(y);
        gt[y].push_back(x);
    }

    use = vector<int>(n + 1, 0);
    for (int i = 1; i <= n; i++)
        if (!use[i])
            dfs(i);

    use = vector<int>(n + 1, 0);
    for (int i : topo)
        if (!use[i]) {
            dfst(i, cnt);
            cnt++;
        }

    cout << cnt << endl;
    for (int i = 0; i < cnt; i++, cout << endl)
        for (int j : group[i])
            cout << j << " ";

    return 0;
}