#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m, s = 0, i, j, k = 0;
  cin >> n >> m;
  vector<int> a(n);
  vector<int> b;
  for (i = 0; i < n; i++) cin >> a[i];
  sort(a.begin(), a.end());
  i = 0;
  for (j = 1;; j++) {
    if (j == a[i])
      i++;
    else if (s <= m - j) {
      s += j;
      b.push_back(j);
      k++;
    } else
      break;
  }
  cout << k << "\n";
  for (i = 0; i < k; i++) cout << b[i] << " ";
  return 0;
}
