#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, ans = 0, have[100100], i, j, way[100100] = {0};
  scanf("%d %d", &n, &m);
  for (i = 0; i < n; i++) scanf("%d", &have[i]);
  sort(have, have + n);
  for (i = 1, j = 0;; i++) {
    if (have[j] == i && j < n) {
      j++;
      continue;
    }
    if (ans + i > m) break;
    ans += i;
    way[++way[0]] = i;
  }
  printf("%d\n", way[0]);
  for (i = 1; i <= way[0]; i++) {
    printf("%d", way[i]);
    if (i != way[0])
      putchar(' ');
    else
      putchar('\n');
  }
  return 0;
}
