#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  long long m;
  scanf("%d", &n);
  cin >> m;
  vector<long long> a(n + 1);
  for (int i = 0; i < n; i++) cin >> a[i];
  a[n] = INT_MAX;
  sort(a.begin(), a.end());
  long long s = 0;
  int i = 0;
  long long cur = 0;
  vector<long long> v;
  while (true) {
    cur++;
    if (a[i] <= cur) {
      i++;
      continue;
    }
    if (cur + s > m) break;
    s += cur;
    v.push_back(cur);
  }
  printf("%d\n", v.size());
  for (int i = 0; i < v.size(); i++) cout << v[i] << ' ';
  return 0;
}
