#include <bits/stdc++.h>
using namespace std;
int a[100005], ans[100005] = {0};
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  sort(a + 1, a + 1 + n);
  a[0] = 0;
  a[n + 1] = 1000000001;
  int remain = m;
  for (int i = 1; i <= n + 1; i++) {
    for (int j = a[i - 1] + 1; j < a[i]; j++) {
      if (j > remain) break;
      remain -= j;
      ans[0]++;
      ans[ans[0]] = j;
    }
  }
  printf("%d\n", ans[0]);
  for (int i = 1; i < ans[0]; i++) printf("%d ", ans[i]);
  if (ans[0] > 0) printf("%d\n", ans[ans[0]]);
  return 0;
}
