#include <bits/stdc++.h>
using namespace std;
long long n, m, ans;
vector<int> v;
long long last = 1;
long long a[100001];
int main() {
  cin >> n >> m;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
  }
  sort(a + 1, a + n + 1);
  for (int i = 1; i <= n; ++i) {
    bool t = false;
    for (int j = last; j < a[i]; ++j) {
      if (j <= m) {
        ++ans;
        m -= j;
        v.push_back(j);
      } else {
        t = true;
        break;
      }
    }
    if (t == true) break;
    last = a[i] + 1;
  }
  last = a[n] + 1;
  while (last <= m) {
    v.push_back(last);
    ++ans;
    m -= last;
    last++;
  }
  cout << ans << '\n';
  for (int i = 0; i < v.size(); ++i) cout << v[i] << " ";
}
