#include <stdio.h>
#define MAX 1000042

int M, N, zrusene_diff[MAX];
FILE *fr, *fw;

int main(void) {
  fr=fopen("mrkev.in", "r");
  fw=fopen("mrkev.out","w");

  fscanf(fr, "%d%d", &M, &N);
  int last=0, zrusene_celkem=0;
  for (int i=0; i<N; i++) {
    int next; fscanf(fr, "%d", &next);
    int length = next - last - 1;
    if (length >= M) {
      zrusene_celkem += (length/M)-1;
      length %= M;
      int s = last % M;
      if (s+length >= M) {
        zrusene_diff[s]++; zrusene_diff[M]--;  /* tohle je zbytečné */
        zrusene_diff[0]++; zrusene_diff[s+length-M+1]--;
      } else {
        zrusene_diff[s]++; zrusene_diff[s+length+1]--;
      }
    }
    last = next;
  }
  fclose(fr);

  int zrusene = 0, best = (1U<<31)-1;
  for (int i=0; i<M; i++) {
    zrusene += zrusene_diff[i];
    int curr = (last-i+M-1)/M - zrusene - zrusene_celkem;
    if (curr < best) best=curr;
  }
  fprintf(fw, "%d\n", best);
  zrusene = 0;
  for (int i=0, uz=0; i<M; i++) {
    zrusene += zrusene_diff[i];
    int curr = (last-i+M-1)/M - zrusene - zrusene_celkem;
    if (curr == best) uz++ && fputc(' ', fw), fprintf(fw, "%d", i+1);
  }
  fputc('\n', fw);
  fclose(fw);
  
  return 0;
}