#include <fstream>
#include <vector>
#define NMAX 100001
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int> G[NMAX],Gt[NMAX],rez[NMAX];
int postordine[NMAX],parcurs[NMAX],parcurs_Gt[NMAX];
int nrp,n,m;

void DFS(int k);
void DFS_Gt(int k);
void citire();

int main()
{
    citire();
    int i;
    for(i=1;i<=n;i++)
        if(!parcurs[i])
        {
            DFS(i);
            postordine[nrp++]=i;
        }
    nrp=0;
    for(i=n-1;i>=0;i--)
        if(!parcurs_Gt[postordine[i]])
        {
            DFS_Gt(postordine[i]);
            nrp++;
        }
    /*for(i=0;i<n;i++)
        fout<<postordine[i]<<" ";*/
    fout<<nrp<<"\n";
    int j;
    for(i=0;i<nrp;i++)
    {
        for(j=0;j<rez[i].size();j++)
            fout<<rez[i][j]<<" ";
        fout<<"\n";
    }
    return 0;
}

void citire()
{
    int x,y;
    fin>>n>>m;
    for(int i=0;i<m;i++)
    {
        fin>>x>>y;
        G[x].push_back(y);
        Gt[y].push_back(x);
    }
}

void DFS(int k)
{
    parcurs[k]=1;
    for(int i=0;i<G[k].size();i++)
        if(!parcurs[G[k][i]])
        {
            DFS(G[k][i]);
            postordine[nrp++]=G[k][i];
        }
}

void DFS_Gt(int k)
{
    parcurs_Gt[k]=1;
    rez[nrp].push_back(k);
    for(int i=0;i<Gt[k].size();i++)
        if(!parcurs_Gt[Gt[k][i]])
        {
            parcurs_Gt[Gt[k][i]]=1;
            DFS_Gt(Gt[k][i]);
        }
}