#include <fstream>
#include <vector>
#include <iterator>
#include <stack>

using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");

void DFS1(int s, vector<int> *la,vector<bool> &viz,stack <int> &S)
{
    viz[s]=1;
    for(int i=0; i<la[s].size(); i++)
        if(viz[la[s][i]]==0)
            DFS1(la[s][i],la,viz,S);
    S.push(s);
}
void DFS(vector<int>*la, int n, stack <int> &S)
{
    vector<bool> viz(n+1, 0);
    for (int i=1; i<=n; i++)
        if (viz[i] == 0)
            DFS1(i, la, viz, S);
}
void DFST1(int x, vector<int> *ta,vector<bool> &vizt, int &nr,vector<int>*ctc)
{
    vizt[x]=1;
    ctc[nr].push_back(x);
    for(int i=0; i<ta[x].size(); i++)
        if(vizt[ta[x][i]]==0)
            DFST1(ta[x][i],ta,vizt,nr,ctc);
}
void DFST(vector<int>*ta, int n, stack <int> &S, int &nr,vector<int>*ctc)
{
    vector<bool> vizt(n+1, 0);
    while(!S.empty())
    {
        int x=S.top();
        S.pop();
        if(vizt[x]==0)
        {
            DFST1(x,ta,vizt,nr,ctc);
            nr++;
        }
    }
}
void getT(vector<int>*la, int n, vector<int>*ta)
{

    vector<int>::iterator it;
    for (int i=1; i<=n; i++)
        for(it = la[i].begin(); it != la[i].end(); it++)
        {
            ta[*it].push_back(i);
        }
}
int main()
{
    int n,m,x,y,nr=0;
    fin>>n>>m;
    vector<int>*la;
    vector<int>*ta;
    vector<int>*ctc;
    stack <int> S;
    la=new vector<int>[n+1];
    ta=new vector<int>[n+1];
    ctc=new vector<int>[n+1];
    for(int i=1; i<=m; i++)
    {
        fin>>x>>y;
        la[x].push_back(y);
    }
    getT(la,n,ta);
    DFS(la,n,S);
    DFST(ta,n,S,nr,ctc);
    fout<<nr<<endl;
    vector<int>::iterator it;
    for(int i=0; i<=nr; i++)
    {
        for (it = ctc[i].begin(); it != ctc[i].end(); it++)
            fout << *it << " ";
        fout<<endl;
    }
    return 0;
}