#include <iostream>
#include <fstream>
#include <bitset>
#include <vector>

using namespace std;
typedef vector<int>::iterator iter;
typedef vector<int>::reverse_iterator riter;

#define MAXN 100005

ifstream f("ctc.in");
ofstream g("ctc.out");

int n, m;
vector<int> G[MAXN], Gt[MAXN], order, comp;
bitset<MAXN> viz;
vector< vector<int> > comps;

void topo(int nd)
{
    if (viz[nd] == true) {
        return;
    }
    viz[nd] = true;

    for (iter it = G[nd].begin(); it != G[nd].end(); it++) {
        topo(*it);
    }

    order.push_back(nd);
}

void connex(int nd)
{
    if (viz[nd] == true) {
        return;
    }
    viz[nd] = true;

    for (iter it = Gt[nd].begin(); it != Gt[nd].end(); it++) {
        connex(*it);
    }
    comp.push_back(nd);
}

int main()
{
    f >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y;
        f >> x >> y;
        G[x].push_back(y);
        Gt[y].push_back(x);
    }

    for (int i = 1; i <= n; i++) {
        topo(i);
    }

    viz.reset();
    for (riter it = order.rbegin(); it != order.rend(); it++) {
        if (viz[*it] == false) {
            comp.clear();
            connex(*it);
            comps.push_back(comp);
        }
    }

    g << comps.size() << '\n';
    for (int i = 0; i < comps.size(); i++) {
        for (iter it = comps[i].begin(); it != comps[i].end(); it++) {
            g << *it << ' ';
        }
        g << '\n';
    }

    f.close();
    g.close();
    return 0;
}