#include <bits/stdc++.h>
using namespace std;
int n, m;
int A[100005];
int ANS[100005];
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) scanf("%d", &A[i]);
  A[n] = 2999999999;
  sort(A, A + n);
  int ans = 0;
  int num = 1, k = 0;
  while (m > 0) {
    while (num >= A[k]) {
      if (num == A[k]) num++;
      k++;
    }
    if (m >= num) {
      ANS[ans++] = num;
    }
    m -= num;
    num++;
  }
  printf("%d\n", ans);
  for (int i = 0; i < ans; i++) {
    if (i) printf(" ");
    printf("%d", ANS[i]);
  }
}
