#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f ("ctc.in");
ofstream g ("ctc.out");
const int nmax=1e5+3;
int viz[nmax],usu[nmax],nr,n,m,a,b,nod;
vector <int> v1[nmax],v2[nmax],sol[nmax];
stack <int> st;
void dfs1(int nod)
{
      viz[nod]=1;
      st.push(nod);
      for(int i=0;i<v2[nod].size();++i)
      {
            if(!viz[v2[nod][i]]) dfs1(v2[nod][i]);
      }
}
void dfs2(int nod)
{
      usu[nod]=nr;
      for(int i=0;i<v1[nod].size();++i)
      {
            if(!usu[v1[nod][i]]) dfs2(v1[nod][i]);
      }
}
int main()
{
      f>>n>>m;
      for(int i=1;i<=m;++i)
      {
            f>>a>>b;
            v1[a].push_back(b);
            v2[b].push_back(a);
      }
      for(int i=1;i<=n;++i)
      {
            if(!viz[i]) dfs1(i);
      }
      while(!st.empty())
      {
            nod=st.top();
            st.pop();
            if(!usu[nod])
            {
                  ++nr;
                  dfs2(nod);
            }
      }
      g<<nr<<'\n';
      for(int i=1;i<=n;++i)
      {
            sol[usu[i]].push_back(i);
      }
      for(int i=1;i<=nr;++i)
      {
            for(int j=0;j<sol[i].size();++j) g<<sol[i][j]<<' ';
            g<<'\n';
      }
      return 0;
}