#include <fstream>
#include <vector>
#include <bitset>
#define nmax 100007
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");

vector <int> g[nmax];
vector <int> gr[nmax];
int post[nmax];
int v[nmax];
int z[nmax];
int nn=0;
int contor=0,cnt=0;

void dfs_graf_invers(int nod)
{
    v[nod]=1;
    for(int i=0;i<gr[nod].size();i++)
    {
        if(v[gr[nod][i]]==0)
            dfs_graf_invers(gr[nod][i]);
    }
    post[++nn]=nod;
}

void dfs(int nod)
{
    z[nod]=contor;
    v[nod]=0;
    for(int i=0;i<g[nod].size();i++)
    {
        if(v[g[nod][i]])
            dfs(g[nod][i]);
    }
}

int main()
{
    int n,m,x,y;
    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        g[x].push_back(y);
        gr[y].push_back(x);
    }
    for(int i=1;i<=n;i++)
    {
        if(v[i]==0)
        {
            dfs_graf_invers(i);
        }
    }
    contor=0;
    for(int i=n;i>=1;i--)
    {
        if(v[post[i]])
        {
            contor++;
            dfs(post[i]);
        }
    }
    fout<<contor<<"\n";
    for(int i=contor;i>=1;i--)
    {
        for(int j=1;j<=n;j++)
        {
            if(z[j]==i)
                fout<<j<<" ";
        }
        fout<<"\n";
    }
    return 0;
}