# include <fstream>
# include <vector>
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
int n, i, j, m, x, nctc, y, viz[100001], ctc[100001];
vector<vector<int>> v, rv, ctcs;
vector<int> order;
void dfs(int x)
{
    viz[x] = 1;
    for (int i = 0; i < v[x].size(); i++)
    {
        if (viz[v[x][i]] == 0)
            dfs(v[x][i]);
    }
    order.push_back(x);
}
void dfs_t(int x)
{
    ctc[x] = nctc;
    for (int i = 0; i < rv[x].size(); i++)
    {
        if (ctc[rv[x][i]] == 0)
            dfs_t(rv[x][i]);
    }
}
int main()
{
    in >> n >> m; v.resize(n + 1); rv.resize(n + 1);
    for (i = 1; i <= m; i++)
    {
        in >> x >> y;
        v[x].push_back(y);
        rv[y].push_back(x);
    }
    for (i = 1; i <= n; i++)
    {
        if (viz[i] == 0)
            dfs(i);
    }
    for (i = n - 1; i >= 0; i--)
    {
        if (ctc[order[i]] == 0)
        {
            nctc++;
            dfs_t(order[i]);
        }
    }
    ctcs.resize(nctc + 1);
    for (i = 1; i <= n; i++)
        ctcs[ctc[i]].push_back(i);
    out << nctc << '\n';
    for (i = 1; i <= nctc; i++, out << '\n')
        for (j = 0; j < ctcs[i].size(); j++)
            out << ctcs[i][j] << ' ';
    return 0;
}