#include <algorithm>
#include <fstream>
#include <stack>
#include <vector>

std::vector<std::vector<unsigned>> graph;
std::vector<int> index;
std::vector<int> lowlink;
std::vector<bool> isOnStack;
std::vector<std::vector<unsigned>> components;

unsigned count = 0;
std::stack<unsigned> s;

void strongConnect(unsigned n) {
  index[n] = count;
  lowlink[n] = count;
  count++;
  isOnStack[n] = true;
  s.push(n);
  for (unsigned w : graph[n]) {
    if (index[w] == -1) {
      strongConnect(w);
      lowlink[n] = std::min(lowlink[n], lowlink[w]);
    } else if (isOnStack[w]) {
      lowlink[n] = std::min(lowlink[n], index[w]);
    }
  }
  if (lowlink[n] == index[n]) {
    components.push_back(std::vector<unsigned>());
    unsigned w;
    do {
      w = s.top();
      s.pop();
      isOnStack[w] = false;
      components[components.size() - 1].push_back(w);
    } while (w != n);
  }
}

int main() {
  std::ifstream in("ctc.in");
  std::ofstream out("ctc.out");

  unsigned n, m;
  in >> n >> m;
  
  graph.reserve(n);
  index.reserve(n);
  lowlink.reserve(n);
  isOnStack.reserve(n);
  for (unsigned i = 0; i < n; i++) {
    graph.push_back(std::vector<unsigned>());
    index.push_back(-1);
    lowlink.push_back(-1);
    isOnStack.push_back(false);
  }
  for (unsigned i = 0; i < m; i++) {
    unsigned from, to;
    in >> from >> to;
    graph[from - 1].push_back(to - 1);
  }
  
  for (int i = 0; i < n; i++) {
    if (index[i] == -1) {
      strongConnect(i);
    }
  }
  
  out << components.size() << "\n";
  for (auto c : components) {
    for (auto n : c) {
      out << n + 1 << " ";
    }
    out << "\n";
  }

  return 0;
}