#include <bits/stdc++.h>

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

int n, viz[100005], nrcc, st[100005], top;
vector <int> h[100005], g[100005], ctc[100005];

void Citire()
{
    int m, x, y;
    fin >> n >> m;
    while (m--)
    {
        fin >> x >> y;
        h[x].push_back(y);
        g[y].push_back(x);
    }
    fin.close();
}

void Afisare()
{
    fout << nrcc << "\n";
    for (int i = 1; i <= nrcc; i++)
    {
        for (int w : ctc[i])
            fout << w << " ";
        fout << "\n";
    }
    fout.close();
}

void DFS(int k)
{
    viz[k] = 1;
    for (int w : h[k])
        if (!viz[w]) DFS(w);
    st[++top] = k;
}

void DFS_g(int k)
{
    viz[k] = 0;
    for (int w : g[k])
        if (viz[w]) DFS_g(w);
    ctc[nrcc].push_back(k);
}

void SortTop()
{
    for (int i = 1; i <= n; i++)
        if (!viz[i]) DFS(i);
}

void ConstrCTC()
{
    SortTop();
    for (int i = n; i > 0; i--)
        if (viz[st[i]])
        {
            nrcc++;
            DFS_g(st[i]);
        }
}

int main()
{

    Citire();
    ConstrCTC();
    Afisare();

    return 0;
}