#include <bits/stdc++.h>
using namespace std;
vector<long long> v;
vector<long long> vec;
int main() {
  long long n, m, i, x;
  cin >> n >> m;
  for (i = 0; i < n; i++) {
    cin >> x;
    v.push_back(x);
  }
  sort(v.begin(), v.end());
  x = 1;
  for (i = 0; i < n && m > 0;) {
    if (v[i] == x) {
      i++;
      x++;
      continue;
    } else {
      if (m >= x) {
        m = m - x;
        vec.push_back(x);
      } else {
        m = 0;
        break;
      }
    }
    x++;
  }
  while (m) {
    if (m < x) break;
    m = m - x;
    vec.push_back(x);
    x++;
  }
  x = vec.size();
  cout << x << "\n";
  for (i = 0; i < x; i++) cout << vec[i] << " ";
  return 0;
}
