#include <cstdio>
#include <vector>

using std::vector;

const int MAX_N = 100000;
const int MAX_M = 200000;

typedef struct {
  int v, next;
} list;

int N, M, numScc, ss;
int stack[MAX_N + 1];
int adj[MAX_N + 1];
int adjt[MAX_N + 1];
list l[MAX_M + 1];
char seen[MAX_N + 1];
vector <int> comp[MAX_N + 1];

void addEdge(int *adj, int u, int v, int pos) {
  l[pos].v = v;
  l[pos].next = adj[u];
  adj[u] = pos;
}

void dfs(int u) {
  if (!seen[u]) {
    int pos, v;
    seen[u] = 1;
    for (pos = adj[u]; pos; pos = l[pos].next) {
      dfs(l[pos].v);
    }
    stack[ss++] = u;
  }
}

void transpose() {
  int u, pos, next;
  for (u = 1; u <= N; u++) {
    for (pos = adj[u]; pos; pos = next) {
      next = l[pos].next;
      addEdge(adjt, l[pos].v, u, pos);
    }
  }
}

void dfst(int u) {
  if (seen[u]) {
    int pos, v;
    seen[u] = 0;
    comp[numScc].push_back(u);
    for (pos = adjt[u]; pos; pos = l[pos].next) {
      dfst(l[pos].v);
    }
  }
}

void kosaraju() {
  int u;
  for (u = 1; u <= N; u++) {
    if (!seen[u]) {
      dfs(u);
    }
  }

  transpose();

  for (; ss; ss--) {
    u = stack[ss - 1];
    if (seen[u]) {
      numScc++;
      dfst(u);
    }
  }
    fprintf(stderr, "amin");
}

int main(void) {
  int i, u, v;
  vector <int>::iterator it;
  FILE *f = fopen("ctc.in", "r");

  fscanf(f, "%d %d", &N, &M);
  for (i = 1; i <= M; i++) {
    fscanf(f, "%d %d", &u, &v);
    addEdge(adj, u, v, i);
  }
  fclose(f);

  kosaraju();

  freopen("ctc.out", "w", stdout);
  fprintf(stdout, "%d\n", numScc);
  for (i = 1; i <= numScc; i++) {
    for (it = comp[i].begin(); it != comp[i].end(); it++) {
      fprintf(stdout, "%d ", *it);
    }
    fprintf(stdout, "\n");
  }
  fclose(stdout);
  return 0;
}