#include <bits/stdc++.h>
using namespace std;
const int N = 100000 + 10;
int n, m;
map<int, bool> hav;
int main() {
  scanf("%d%d", &n, &m);
  for (int x, i = 0; i < n; ++i) {
    scanf("%d", &x);
    hav[x] = true;
  }
  vector<int> ans;
  for (int i = 1; m >= i; ++i) {
    if (hav[i]) continue;
    m -= i;
    ans.push_back(i);
  }
  printf("%d\n", ans.size());
  for (int i = 0; i < ans.size(); ++i)
    printf("%d%c", ans[i], i + 1 == ans.size() ? '\n' : ' ');
  return 0;
}
