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

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

void Write();
void Tarjan( int k );

int idx, n, m, x, y;
vector<vector<int>> G;
vector<vector<int>> sol;
vector<int> index;
vector<int> L;
vector<int> aux;
vector<bool> instack;
stack<int> Q;

int main()
{
    is >> n >> m;
    G.resize(n+1);
    instack = vector<bool>(n+1);
    index = vector<int>(n+1);
    L = vector<int>(n+1);
    for ( int i = 1; i <= n; i++ )
        index[i] = INF;
    for ( int i = 1; i <= m; i++ )
    {
        is >> x >> y;
        G[x].push_back(y);
    }
    for ( int i = 1; i <= n; i++ )
        if ( index[i] == INF )
            Tarjan( i );
    Write();
    is.close();
    os.close();
    return 0;
}

void Write()
{
    os << sol.size() << '\n';
    for (int i = 0; i < sol.size(); ++i)
    {
        for (int j = 0; j < sol[i].size(); ++j)
            os << sol[i][j] << ' ';
        os << '\n';
    }
}

void Tarjan( int k )
{
    index[k] = L[k] = ++idx;
    Q.push(k);
    instack[k] = true;
    for ( const auto& y : G[k] )
    {
        if ( index[y] == INF )
        {
            Tarjan(y);
            L[k] = min(L[y], L[k]);
        }
        else
        {
            if ( instack[y] )
                L[k] = min(L[y], L[k] );
        }
    }
    int node;
    if ( L[k] == index[k] )
    {
        do
        {
            node = Q.top();
            Q.pop();
            aux.push_back(node);
            instack[node] = false;
        } while( node != k );
        sol.push_back(aux);
        aux.clear();
    }
}