#include <bits/stdc++.h>
using namespace std;
int a[100001];
int main() {
  vector<int> toys;
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  int i = 1, ans = 0;
  while (m > 0) {
    if (binary_search(a, a + n, i)) {
      i++;
      continue;
    } else {
      if (m - i >= 0) {
        m -= i;
        toys.push_back(i);
        i++;
        ans++;
      } else
        break;
    }
  }
  cout << ans << endl;
  for (int j = 0; j < toys.size(); j++) cout << toys[j] << " ";
}
