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

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

using VI = vector<int>;
using VB = vector<bool>;
using VVI = vector<VI>;

int n, m;
VB ok;
VI nv, nm, comp;
VVI g, ctc;
stack<int> s;

void Read();
void Solve(int nod, int niv);
void Write();

int main()
{
    Read();
    nv = nm = VI(n + 1);
    ok = VB(n + 1);
    for ( int i = 1; i <= n; ++i )
        if ( !nv[i] )
            Solve(i, 1);
    Write();
    is.close();
    os.close();
    return 0;
}

void Solve(int nod, int niv)
{
    nv[nod] = nm[nod] = niv;
    ok[nod] = true;
    s.push(nod);
    for ( const auto& nodv : g[nod] )
    {
        if ( !nv[nodv] )
        {
            Solve(nodv, niv + 1);
            nm[nod] = min(nm[nod], nm[nodv]);
        }
        else
            if ( ok[nodv] )
                nm[nod] = min(nm[nod], nm[nodv]);
    }
    if ( nv[nod] == nm[nod] )
    {
        comp.clear();
        int n2;
        do
        {
            comp.push_back(n2 = s.top());
            ok[n2] = false;
            s.pop();
        } while ( n2 != nod );
        ctc.push_back(comp);
    }
}

void Read()
{
    is >> n >> m;
    g = VVI(n + 1);
    int n1, n2;
    while ( m-- )
    {
        is >> n1 >> n2;
        g[n1].push_back(n2);
    }
}

void Write()
{
    os << ctc.size() << "\n";
    for ( const auto& i : ctc )
    {
        for ( const auto& j : i )
            os << j << " ";
        os << "\n";
    }
}