#include <bits/stdc++.h>

using namespace std;

const int MAXN = 1e5;

vector < int > g[MAXN + 1], gt[MAXN + 1], ord;
vector < vector < int > > ctc;
int seen[MAXN + 1];

void norm_dfs(int node) {
  seen[node] = 1;
  for (auto it : g[node])
    if (seen[it] == 0)
      norm_dfs(it);
  ord.push_back(node);
}

void rev_dfs(int node, vector < int >& comp) {
  seen[node] = 0;
  comp.push_back(node);
  for (auto it : gt[node])
    if (seen[it])
      rev_dfs(it, comp);
}

int main()
{
    int n, m;
    ifstream fin("ctc.in");
    fin >> n >> m;
    for (int i = 0; i < m; ++i) {
      int x, y;
      fin >> x >> y;
      g[x].push_back(y);
      gt[y].push_back(x);
    }
    fin.close();
    for (int i = 1; i <= n; ++i)
      if (seen[i] == 0)
        norm_dfs(i);
    while (ord.empty() == false) {
      if (seen[ord.back()]) {
        vector < int > comp;
        rev_dfs(ord.back(), comp);
        ctc.push_back(comp);
      }
      ord.pop_back();
    }
    ofstream fout("ctc.out");
    fout << ctc.size() << '\n';
    for (auto comp : ctc) {
      for (auto it : comp)
        fout << it << " ";
      fout << '\n';
    }
    fout.close();
    return 0;
}