#include <bits/stdc++.h>
using namespace std;
int number[100005];
int ans[100005];
int main() {
  int n, m, k = 0, flag = 0;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) {
    scanf("%d", &number[i]);
  }
  sort(number, number + n);
  for (int i = 1; i < number[0]; i++) {
    if (m - i >= 0) {
      m = m - i;
      ans[k++] = i;
    } else
      break;
  }
  for (int i = 0; i < n - 1; i++) {
    for (int j = number[i] + 1; j < number[i + 1]; j++) {
      if (m - j >= 0) {
        m = m - j;
        ans[k++] = j;
      } else {
        flag = 1;
        break;
      }
    }
    if (flag == 1) break;
  }
  for (int i = number[n - 1] + 1;; i++) {
    if (m - i >= 0) {
      m = m - i;
      ans[k++] = i;
    } else
      break;
  }
  printf("%d\n", k);
  if (k == 0)
    return 0;
  else {
    for (int i = 0; i < k - 1; i++) printf("%d ", ans[i]);
    printf("%d", ans[k - 1]);
  }
  return 0;
}
