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

using namespace std;

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

const int N = 1e5;
bool viz[N + 1];

vector <int> g[N + 1], gt[N + 1], l[N + 1], v;

int n, m, len, x, y;

void dfsplus (int node)
{
    viz[node] = 1;
    for (auto it : g[node])
        if (!viz[it])
            dfsplus (it);
    v.push_back(node);
}

void dfsminus (int node)
{
    viz[node] = 1;
    l[len].push_back(node);
    for (auto it : gt[node])
        if (!viz[it])
            dfsminus (it);
}
int main()
{
    cin >> n >> m;
    for (int i = 1; i <= m; ++i)
    {
        cin >> x >> y;
        g[x].push_back(y);
        gt[y].push_back(x);
    }
    for (int i = 1; i <= n; ++i)
        if (!viz[i])
            dfsplus(i);
    reverse (v.begin(), v.end());
    for (int i = 1; i <= n; ++i)
        viz[i] = 0;
    for (auto it : v)
        if (!viz[it])
            ++len, dfsminus (it);
    cout << len << '\n';
    for (int i = 1; i <= len; ++i, cout << '\n')
        for (auto it : l[i])
            cout << it << ' ';
    return 0;
}