#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  set<int> a;
  for (int i = 0, x; i < n; i++) {
    scanf("%d", &x);
    a.insert(x);
  }
  vector<int> ans;
  for (int i = 1; i <= 1000000; i++) {
    if (i <= m) {
      if (a.find(i) == a.end()) {
        m -= i;
        ans.push_back(i);
      }
    } else
      break;
  }
  printf("%d\n", ans.size());
  for (int i = 0; i < ans.size(); i++) {
    printf("%d ", ans[i]);
  }
  cout << "";
  return 0;
}
