#include <iostream>
#include <fstream>
#include <vector>

using namespace std;
vector <int> G[100010],Gt[100010],sol[100010];
int n,m,viz[100100],V[100100],k=0;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
void citire()
{
    int x, y;
    fin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        fin>>x>>y;
        G[x].push_back(y);
        Gt[y].push_back(x);
    }
}
void dfs(int x)
{
    viz[x]=1;
    for(auto &v:G[x])
    {
        if(viz[v]==0)
            dfs(v);
    }
    V[++k]=x;
}
void rezolva(int x,int y)
{
    viz[x]=0;
    sol[y].push_back(x);
    for(auto &v:Gt[x])
    {
        if(viz[v]==1)
            rezolva(v,y);
    }
}
int main()
{
    citire();
    int nr=0;
    for(int i=1; i<=n; i++)
    {
        if(viz[i]==0)
            dfs(i);
    }
    for(int i=k; i>=1; i--)
    {
        if(viz[V[i]]==1)
        {
            rezolva(V[i],nr+1);
            nr++;
        }
    }
    fout<<nr<<endl;
    for(int i=1; i<=nr+1; i++)
    {
        for(auto &v: sol[i])
            fout<<v<<" ";
        fout<<endl;
    }

    return 0;
}