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

int n, m;
vector <int> g[100001], invg[100001], comp[100001];
bool viz[100001];

void dfs(int node, vector <int> &sorted)
{
    viz[node] = true;
    for (auto vecin : g[node])
    {
        if (!viz[vecin])
        {
            dfs(vecin, sorted);
        }
    }
    sorted.push_back(node);
}

void det_comp(int node, vector <int> &comp)
{
    for (auto vecin : invg[node])
        if (viz[vecin])
        {
            viz[vecin] = false;
            comp.push_back(vecin);
            det_comp(vecin, comp);
        }
}

void topo_sort(vector <int> &sorted)
{
    for (int node = 1; node <= n; node++)
    {
        if (!viz[node])
            dfs(node, sorted);
    }
    reverse(sorted.begin(), sorted.end());
}

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


    vector <int> sortat;
    topo_sort(sortat);

    int nrcomp = 0;
    for (auto node : sortat)
        if (viz[node])
            det_comp(node, comp[++nrcomp]);

    fout << nrcomp << '\n';
    for (int i = 1; i <= nrcomp; i++)
    {
        for (auto node : comp[i])
            fout << node << ' ';
        fout << '\n';
    }
    return 0;
}