#include <bits/stdc++.h>
using namespace std;
const int N = (4e5 + 5);
vector<int> ans;
int i, n, s, x;
bool ap[N];
int main() {
  scanf("%d%d", &n, &s);
  for (i = 1; i <= n; ++i) {
    scanf("%d", &x);
    if (x <= N - 5) ap[x] = 1;
  }
  for (i = 1; i <= N - 5; ++i)
    if (!ap[i] && s >= i) s -= i, ans.push_back(i);
  printf("%d\n", ans.size());
  for (i = 0; i < ans.size(); ++i) printf("%d ", ans[i]);
  return 0;
}
