#include <fstream>
#include <vector>
#include <stack>
#include <bitset>
#define INF 0x3f3f3f3f
using namespace std;

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

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

int n, m, cnt;
VI c, nv, nm;
VVI g, ctc;
stack<int> s;
bitset<100001> ok;

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

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

void Tarjan(int nod)
{
    nv[nod] = nm[nod] = ++cnt;
    ok[nod] = 1;
    s.push(nod);
    for ( const auto &nodv : g[nod] )
        if ( !nv[nodv] )
        {
            Tarjan(nodv);
            nm[nod] = min(nm[nod], nm[nodv]);
        }
        else
            if ( ok[nodv] )
                nm[nod] = min(nm[nod], nv[nodv]);
    if ( nv[nod] == nm[nod] )
    {
        c.clear();
        int nod2;
        do {
            c.push_back(nod2 = s.top());
            ok[nod2] = 0;
            s.pop();
        } while ( nod != nod2 );
        ctc.push_back(c);
    }
}

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

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