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

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

int n, m, cnt;
vector<vector<int> > g, ctc;
vector<int> index, gmin, comp;
vector<bool> ok;
stack<int> s;

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

int main()
{
    Read();
    for ( int i = 1; i <= n; ++i )
        if ( !index[i] )
            Solve(i);
    Write();
    is.close();
    os.close();
    return 0;
}

void Solve(int nod)
{
    index[nod] = gmin[nod] = ++cnt;
    ok[nod] = true;
    s.push(nod);
    for ( const auto& nodv : g[nod] )
    {
        if ( !index[nodv] )
        {
            Solve(nodv);
            gmin[nod] = min(gmin[nod], gmin[nodv]);
        }
        else
            if  ( ok[nodv] )
                gmin[nod] = min(gmin[nod], index[nodv]);
    }
    if ( index[nod] == gmin[nod] )
    {
        comp.clear();
        int nod2;
        do
        {
            comp.push_back(nod2 = s.top());
            s.pop();
            ok[nod2] = false;
        } while ( nod != nod2 );
        ctc.push_back(comp);
    }
}

void Read()
{
    int n1, n2;
    is >> n >> m;
    g.resize(n + 1);
    index.resize(n + 1);
    gmin.resize(n + 1);
    ok.resize(n + 1);
    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";
    }
}