#include <fstream>
#include <vector>
using namespace std;
#define nmax 100005

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

int viz[nmax], s[nmax], n, m, len;
vector<int> ctc[nmax]; 
vector<int> L[nmax];
vector<int> T[nmax];
int nrc; 

void read()
{
    int i, j, k;
    f >> n >> m;
    for (k = 1; k <= m; k++)
    {
        f >> i >> j;
        L[i].push_back(j);
        T[j].push_back(i);
    }
}

void first(int k)
{
    viz[k] = 1;
    for (int i : L[k])
        if (viz[i] == 0) first(i);
    s[++len] = k;
}

void FirstRun()
{
    for (int k = 1; k <= n; k++)
        if (viz[k] == 0)
            first(k);
}

void zero()
{
    for (int i = 1; i <= n; i++)
        viz[i] = 0;
}

void second(int k)
{
    viz[k] = nrc;
    for (int i : T[k])
        if (viz[i] == 0) second(i);
    ctc[nrc].push_back(k);
}

void Kosaraju()
{
    for (int k = n; k >= 1; k--)
        if (viz[s[k]] == 0)
        {
            nrc++;
            second(s[k]);
        }
}

void print()
{
    g << nrc << "\n";
    for (int k = 1; k <= nrc; k++)
    {
        for (int i : ctc[k])
            g << i << " ";
        g << "\n";
    }
}

int main()
{
    read();
    FirstRun();
    zero();
    Kosaraju();
    print();
    return 0;
}