#include <fstream>
#include <stack>
#include <vector>

using namespace std;

ifstream f("ctc.in");
ofstream g("ctc.out");
int n,m,k,ctc,nod;
stack<int> s;
vector<int> index, lowl;
vector<bool> inStiva;
vector<vector<int>> adiac;

void tarjan(int v)
{
    s.push(v);
    inStiva[v] = true;
    index[v] = k;
    lowl[v] = k;
    k++;

    for(auto vec : adiac[v])
        {
        if (index[vec] == -1)
            tarjan(vec);
        if (inStiva[vec] == true)
            lowl[v] = min(lowl[v],lowl[vec]);
        }

    if(lowl[v] == index[v])
        {
         do
            {
            nod = s.top();
            lowl[nod] = index[v];
            inStiva[nod] = false;
            s.pop();
            }while(nod!=v);
         ctc++;
        }

}

void afis(vector<int>lowl)
{
    g<<ctc<<"\n";
    int k=0,ok;

    for (int i = 0; i < n && k != n; i++)
        {ok=0;
         for (int j = 1; j <= n && k != n; j++)
            {
             if(lowl[j] == i)
                {
                 g << j << " ";
                 k++;
                 ok=1;
                }
            }
            if(ok)
                g << "\n";
        }
}

int main()
{
    int a, b;
    f >> n >> m;

    index.resize(n+1); index.assign(n+1,-1);
    lowl.resize(n+1); lowl.assign(n+1,-1);
    inStiva.resize(n+1); inStiva.assign(n+1,false);
    adiac.resize(n+1);

    for (int i = 0; i < m; i++)
        {
         f >> a >> b;
         adiac[a].push_back(b);
        }

    for (int i = 1; i <= n; i++)
        {
         if(index[i] == -1)
            tarjan(i);
        }

    afis(lowl);

    return 0;
}