#include <fstream>
#include <vector>

const int nmax = 1e5 + 5;

std::vector<int>in[nmax], out[nmax], ans[nmax], st;
int viz[nmax], k;

void dfs(int node, int type) {
 viz[node] = type;
 if (type == 1) {
  for (auto x : in[node]) if (viz[x] == 0) dfs(x, type);
  st.push_back(node);
 }
 else {
  ans[k].push_back(node);
  for (auto x : out[node]) if (viz[x] == 1) dfs(x, type);
 }
}

int main() {
 std::ifstream fin("ctc.in");
 std::ofstream fout("ctc.out");
 int n, m, u, v;
 fin >> n >> m;
 for (int i = 0; i < m; i++) {
  fin >> u >> v;
  in[u].push_back(v);
  out[v].push_back(u);
 }
 for (int i = 1; i <= n; i++)
  if (!viz[i]) dfs(i, 1);
 while (st.size()) {
  int node = st.back();
  st.pop_back();
  if (viz[node] == 1) k++, dfs(node, 2);
 }
 fout << k;
 for (int i = 1; i <= k; i++) {
  fout << "\n";
  for (auto x : ans[i])
   fout << x << " ";
 }
}