#include <iostream>
#include <fstream>
#include <algorithm>
#include <stack>
#include <vector>
using namespace std;

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

stack <int>s;

vector <int>v[100005] , vtr[100005];

int ctc = 0 , viz[100005] , vecin , x , y , n , m;

void dfs (int nod)
{
    viz[nod] = 1;
    for (auto vecin : v[nod])
        if (viz[vecin] == 0)
            dfs (vecin);

    s.push (nod);
}

void dfst (int nod , int niv)
{
    viz[nod] = niv;
    for (auto vecin : vtr[nod])
        if (viz[vecin] == 1)
         dfst (vecin , niv);
}

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

    for (int i = 1 ; i <= n ; i++)
        if (viz[i] == 0)
            dfs (i);
    ctc = 1;
    while (!s.empty())
    {
        int nod = s.top ();
        s.pop ();
        if (viz[nod] == 1)
            ctc++ , dfst (nod , ctc);
    }
    g << ctc - 1 << '\n';;
    for (int i = 2 ; i <= ctc ; i++)
    {
        for (int j = 1 ; j <= n ; j++)
              if (viz[j] == i)
                g << j << " ";
          g << '\n';
    }
    return 0;
}