#include <bits/stdc++.h>
#define in "ctc.in"
#define out "ctc.out"
#define Nmax 100003
using namespace std;
ifstream fin(in);
ofstream fout(out);

int n,m;
int viz[Nmax];
vector <int> L[Nmax];
vector <int> T[Nmax];
int st[Nmax],top;
int ctc[Nmax],nrcon;

void Read()
{
    int i,x,y;

    fin >> n >> m;
    for (i = 1; i <= m; i++)
    {
        fin >> x >> y;
        L[x].push_back(y);
        T[y].push_back(x);
    }
}

void DFSt(int k)
{
    viz[k] = 1;
    ctc[k] = nrcon;
    for (auto i : T[k])
        if (viz[i] == 0 && ctc[i] == 0) DFSt(i);
}

void DFS_tf(int k)
{
    viz[k] = 1;
    for (auto i : L[k])
        if (viz[i] == 0) DFS_tf(i);
    top++;
    st[top] = k;
}

void CTC()
{
    int i,k;

    for (i = 1; i <= n; i++)
        if (viz[i] == 0) DFS_tf(i);

    for (i = 1; i <= n; i++)
        viz[i] = 0;

    while (top > 0)
    {
        k = st[top--];

        if (ctc[k] == 0)
        {
            nrcon++;
            DFSt(k);
        }
    }
}

void Afis()
{
    int i,nr = 1;

    fout << nrcon << "\n";
    sort(ctc+1,ctc+n+1);
    for (i = 1; i <= n; i++)
        if (ctc[i] == nr) fout << i << " ";
        else
        {
            nr++;
            i--;
            fout << "\n";
        }
}

int main()
{
    Read();
    CTC();
    Afis();

    fin.close();
    fout.close();
    return 0;
}