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

using namespace std;

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

const static int nmax = 5001;

int n , m;
int mat[nmax][nmax];
bool sel[nmax];

vector <int> numere;

void DF(int nod)
{
    sel[nod] = true;
    numere.push_back(nod);
    for (int i = 1;i<=n;i++)
    {
        if (mat[nod][i] && mat[i][nod] && !sel[i])
        {
            DF(i);
        }
    }
}

int main()
{
    in >> n >> m;

    for (int i =1;i<=n;i++)
        for (int j =1;j<=n;j++)
            mat[i][j] = 0;

    for (int i =0;i<m;i++)
    {
        int x , y;
        in >> x >> y;
        mat[x][y] = 1;
    }


    for (int i =1;i<=n;i++)
        for (int j =1;j<=n;j++)
            for (int k =1;k<=n;k++)
            {
                if (mat[i][k] && mat[k][j] && i !=j) mat[i][j] = 1;
            }

    fill(sel,sel+nmax,false);
    int nr = 0;
    for (int i =1;i<=n;i++)
    {
        if (!sel[i])
        {
            nr++;
            DF(i);
            numere.push_back(-1);
        }
    }

    out << nr << "\n";
    for (int i =0;i<numere.size();i++)
    {
        if (numere[i] == -1)
        {
            out << "\n";
        }
        else
        {
            out << numere[i] << " ";
        }
    }
    in.close();
    out.close();

    return 0;
}