#include <bits/stdc++.h>
using namespace std;
const double PI = 2 * acos(0.0);
int dx[] = {0, 1, 0, -1};
int dy[] = {1, 0, -1, 0};
void fastInOut();
long long pwr(long long base, long long power) {
  long long res = 1;
  while (power) {
    if (power & 1) res *= base;
    base *= base;
    power >>= 1;
  }
  return res;
}
int comp_double(double a, double b) {
  if (fabs(a - b) <= 1e-10) return 0;
  return a < b ? -1 : 1;
}
int main() {
  fastInOut();
  int n, k, x;
  cin >> n >> k;
  vector<int> v, res;
  while (n--) {
    cin >> x;
    v.push_back(x);
  }
  sort(v.begin(), v.end());
  for (int i = 1, r = 0;; i++) {
    if (k - i < 0) break;
    if (r < v.size()) {
      if (v[r] != i)
        res.push_back(i), k -= i;
      else
        r++;
    } else
      res.push_back(i), k -= i;
  }
  cout << res.size() << endl;
  for (auto i : res) cout << i << " ";
}
void fastInOut() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL), cout.tie(NULL);
}
