#include <bits/stdc++.h>
using namespace std;
map<int, bool> a;
int b[50000], l = 0;
int main() {
  int n, s, k;
  scanf("%d %d", &n, &s);
  for (int i = 0; i < n; i++) {
    scanf("%d", &k);
    a[k] = 1;
  }
  int i = 1;
  int sum = 0;
  while (1) {
    if (a[i] == 0) {
      if (sum + i <= s) {
        sum += i;
        b[l++] = i;
      } else
        break;
    }
    i++;
  }
  printf("%d\n", l);
  for (int j = 0; j < l; j++) printf("%d ", b[j]);
  return 0;
}
