#include <stdio.h>
#include <algorithm>
#include <vector>

const int MAX_N = 100000;

std::vector<int> neighbours[1 + MAX_N];
std::vector<int> neighboursT[1 + MAX_N];

bool visited[1 + MAX_N];
std::vector<int> dfsOrder;

int sccCount;
std::vector<int> sccs[MAX_N];

void dfs(int u) {
  visited[u] = true;
  for (int v : neighbours[u])
    if (!visited[v])
      dfs(v);
  dfsOrder.push_back(u);
}

void dfsT(int u, int label) {
  visited[u] = true;
  sccs[label].push_back(u);
  for (int v : neighboursT[u])
    if (!visited[v])
      dfsT(v, label);
}

int main() {
  freopen("ctc.in", "r", stdin);
  freopen("ctc.out", "w", stdout);
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < m; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    neighbours[u].push_back(v);
    neighboursT[v].push_back(u);
  }
  for (int u = 1; u <= n; u++)
    visited[u] = false;
  for (int u = 1; u <= n; u++)
    if (!visited[u])
      dfs(u);
  std::reverse(dfsOrder.begin(), dfsOrder.end());
  for (int u = 1; u <= n; u++)
    visited[u] = false;
  sccCount = 0;
  for (int u : dfsOrder)
    if (!visited[u]) {
      dfsT(u, sccCount);
      sccCount++;
    }
  printf("%d\n", sccCount);
  for (int i = 0; i < sccCount; i++) {
    for (int u : sccs[i])
      printf("%d ", u);
    printf("\n");
  }
  return 0;
}