#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;

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

int n, m, nr, nr2, viz[100001];
vector<int> G[100001], GT[100001], afis[100001];
stack<int> f;

void dfs(int x) {
    viz[x] = 1;
    for (int i : G[x])
        if (!viz[i])
            dfs(i);
    f.push(x);
}

void dfs_t(int x) {
    viz[x] = 1;
    for (int i : GT[x])
        if (!viz[i]) {
            afis[nr].push_back(i);
            dfs_t(i);
        }
}

int main()
{
    fin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y;
        fin >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
    // Parcurgem G si determinam pt fiecare x nodul final f[x]
    for (int i = 1; i <= n; i++)
        if (!viz[i])
            dfs(i);
    for (int i = 1; i <= n; i++)
        viz[i] = 0;
    // Pargurgem GT din f[] in ordine descrescatoare
    while (!f.empty()) {
        int tmp = f.top();
        f.pop();
        if (!viz[tmp]) {
            nr++;
            afis[++nr2].push_back(tmp);
            dfs_t(tmp);
        }
    }

    fout << nr << "\n";
    for (int i = 1; i <= nr; i++) {
        for (int tmp : afis[i])
            fout << tmp << " ";
        fout << "\n";
    }
    return 0;
}