#include <bits/stdc++.h>
using namespace std;
int n, m, k, l, r, a[111111];
string s;
vector<int> ans;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> n >> m;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
  }
  sort(a, a + n + 1);
  k = 1;
  int j = 1;
  a[n + 1] = 1e9;
  a[n + 1]++;
  while (true) {
    if (a[j] == k) {
      j++;
    } else {
      if (m - k >= 0) {
        m -= k;
        ans.push_back(k);
      } else
        break;
    }
    k++;
  }
  cout << ans.size() << "\n";
  for (int i = 0; i < ans.size(); ++i) {
    cout << ans[i] << ' ';
  }
}
