#include <fstream>
#include <vector>
#include <algorithm>
#define NMAX 100005

using namespace std;

ifstream f("ctc.in");
ofstream g("ctc.out");

int i, n, m, x, y, level = 0, sol[NMAX];
bool used[NMAX];
vector < int > v[2 * NMAX], vt[2 * NMAX], ans[2 * NMAX];
//vector < int > :: iterator it;

void DFS(int node)
{
    used[node] = 1;

    for (vector < int > :: iterator it = v[node].begin(); it != v[node].end(); ++ it)
        if (!used[*it])
            DFS(*it);

    sol[++ level] = node;
}

void DFS2(int node)
{
    used[node] = 0;
    ans[level].push_back(node);

    for (vector < int > :: iterator it = vt[node].begin(); it != vt[node].end(); ++ it)
        if (used[*it])
            DFS2(*it);
}

int main()
{
    f >> n >> m;

    for (i = 1; i <= m; ++ i)
    {
        f >> x >> y;
        v[x].push_back(y);
        vt[y].push_back(x);
    }

    for (i = 1; i <= n; ++ i)
        if (!used[i])
            DFS(i);

    level = 0;

    for (i = n; i >= 1; -- i)
        if (used[sol[i]])
        {
            level ++;
            DFS2(sol[i]);
        }

    g << level << '\n';

    for (i = 1; i <= level; ++ i)
    {
        for (vector < int > :: iterator it = ans[i].begin(); it != ans[i].end(); ++ it)
            g << * it << " ";
        g << '\n';
    }

    return 0;
}