#include <fstream>
#include <vector>
#include <Queue>

using namespace std;

ifstream cin("ctc.in");
ofstream cout("ctc.out");

vector<int> Gf[101],Gft[101],Dfs1;

queue<int>Q;

int n,m,nr;

int viz[101],comp[101];

void Citire()
{
    int x=0,y=0;

    cin>>n>>m;

    for(int i=1;i<=m;++i)
    {
        cin>>x>>y;

        Gf[x].push_back(y);
        Gft[y].push_back(x);
    }
}

void DFS(int nod)
{
    viz[nod]=1;

    for(int i=0;i<Gf[nod].size();++i)
    {
        if(viz[Gf[nod][i]]==0)
            DFS(Gf[nod][i]);
    }
    Dfs1.push_back(nod);
}

void DFT(int nod,int c)
{
    viz[nod]=0;

    comp[nod]=c;

    Q.push(nod);

    for(int i=0;i<Gft[nod].size();++i)
    {
        if(viz[Gft[nod][i]]==1)
            DFT(Gft[nod][i],c);
    }
}

int main()
{
    Citire();

    for(int j=1;j<=n;++j)
        if(viz[j]==0)
            DFS(j);

    for(int j=Dfs1.size()-1;j>=0;--j)
        if(viz[Dfs1[j]])
        {
            DFT(Dfs1[j],++nr);
            Q.push(-1);
        }

    cout<<nr<<'\n';

    while(!Q.empty())
    {
        if(Q.front()==-1)
            cout<<'\n';
        else
            cout<<Q.front()<<' ';

        Q.pop();
    }

    return 0;
}