#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, n, m, x;
  set<int> arr, toy;
  scanf("%d%d", &n, &m);
  for (i = 0; i < n; i++) {
    scanf("%d", &x);
    arr.insert(x);
  }
  for (i = 1; i <= m; i++) {
    if (!arr.count(i)) {
      toy.insert(i);
      m -= i;
    }
  }
  x = toy.size();
  printf("%d\n", x);
  for (auto it = toy.begin(); it != toy.end(); it++) printf("%d ", *it);
}
