#include <bits/stdc++.h>
using namespace std;
int i, j, k, l, x, y, z, n, m, ans;
map<int, int> toys;
vector<int> answers;
int main() {
  cin >> n >> m;
  for (i = 0; i < n; i++) {
    scanf("%d", &x);
    toys[x] = 1;
  }
  for (i = 1;; i++) {
    if (toys[i]) continue;
    if (m - i >= 0) {
      answers.push_back(i);
      ans++;
    }
    m = m - i;
    if (m <= i) break;
  }
  printf("%d\n", ans);
  for (i = 0; i < answers.size(); i++) {
    printf("%d ", answers[i]);
  }
  return 0;
}
