#include <fstream>
#include <stack>
#include <vector>
#define NMAX 100002
using namespace std;
ifstream fin ("ctc.in");
ofstream fout ("ctc.out");
vector <int> G[NMAX];
vector <int> Gt[NMAX];
stack <int> stiva; ///punem ca sa nu mai luam descrescator
int n,m,cont;
int uz1[NMAX];
int uz2[NMAX];
vector <int> ctc[NMAX];
void citire()
{
    int x,y;
    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        Gt[y].push_back(x);
         G[x].push_back(y);
    }
}
void dfs1(int k)
{
    uz1[k]=1;
    for(int i=0;i<G[k].size();i++)
        if(!uz1[G[k][i]])
        dfs1(G[k][i]);
    stiva.push(k);
}
void dfs2(int k)
{
    uz2[k]=1;
    ctc[cont].push_back(k);
    for(int i=0;i<Gt[k].size();i++)
        if(!uz2[Gt[k][i]])
        dfs2(Gt[k][i]);
}
int main()
{
    citire();
    for(int i=1;i<=n;i++)
        if(!uz1[i]) dfs1(i);
    while(!stiva.empty())
    {
        int nod=stiva.top();
        if(!uz2[nod])
        {
            cont++;
            dfs2(nod);
        }
        stiva.pop();
    }
    fout<<cont;

    for(int i=1;i<=cont;i++)
    {
          fout<<'\n';
        for(int j=0;j<ctc[i].size();j++)
            fout<<ctc[i][j]<<" ";
    }
    return 0;
}