#include <fstream>
#include <vector>
#include <bitset>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");

int n, m, x, y, sol;
vector < int > direct[100005], invers[100005], ctc[100005], srt;
bitset < 100005 > viz;
vector<int>::iterator it;

void dfsDirect(int nod)
{
    viz[nod]=1;
    for (it=direct[nod].begin(); it!=direct[nod].end(); ++it)
        if (!viz[*it]) dfsDirect(*it);
    srt.push_back(nod);
}

void dfsInvers(int nod)
{
    viz[nod]=0; ctc[sol].push_back(nod);
    for (it=invers[nod].begin(); it!=invers[nod].end(); ++it)
        if (viz[*it]) dfsInvers(*it);
}

int main()
{
    f>>n>>m;
    for (int i=1; i<=m; ++i)
    {
        f>>x>>y;
        direct[x].push_back(y);
        invers[y].push_back(x);
    }

    for (int i=1; i<=n; ++i)
        if (!viz[i]) dfsDirect(i);

    for (int i=srt.size()-1; i>=0; --i)
        if (viz[srt[i]])
            ++sol, dfsInvers(srt[i]);

    g<<sol<<'\n';
    for (int i=1; i<=sol; ++i && g<<'\n')
        for (int j=0; j<(int)ctc[i].size(); ++j)
            g<<ctc[i][j]<<' ';
    return 0;
}