#include <fstream>
#include <vector>

#define NMAX 100005

using namespace std;

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

int n, m;
int x, y;
vector<int> l[NMAX];
vector<int> lt[NMAX];
bool f[NMAX];
vector<int> postord;
int counter;
vector<int> ctc[NMAX];
int i, j;

void bfs(int);
void bfsgt(int);
void bfsgt(int);

int main()
{
    fin >>n>>m;
    for (i = 1; i <= m; ++i)
    {
        fin >>x>>y;
        l[x].push_back(y);
        lt[y].push_back(x);
    }

    for (i = 1; i <= n; ++i)
        if (!f[i]) bfs(i);

    for (i = postord.size()-1; i >= 0; --i)
        if (f[postord[i]])
        {
            counter ++;
            bfsgt(postord[i]);
        }

    fout <<counter<<'\n';
    for (i = 1; i <= counter; ++i)
    {
        for (j = 0; j < ctc[i].size(); ++j)
            fout <<ctc[i][j]<<' ';
        fout <<'\n';
    }
    fout.close();
    return 0;
}

void bfs(int vf)
{
    int i; int vfnou;
    f[vf] = 1;

    for (i = 0; i < l[vf].size(); ++i)
    {
        vfnou = l[vf][i];
        if (!f[vfnou]) bfs(vfnou);
    }
    postord.push_back(vf);
}

void bfsgt(int vf)
{
    int i; int vfnou;
    f[vf] = 0;

    ctc[counter].push_back(vf);
    for (i = 0; i < lt[vf].size(); ++i)
    {
        vfnou = lt[vf][i];
        if (f[vfnou]) bfsgt(vfnou);
    }
}