#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  long long int a[100005], b[100005];
  cin >> n >> m;
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  int sum = 0, count = 0, p = 1, ak = 0;
  while (sum + p <= m) {
    if (p != a[ak]) {
      sum += p;
      b[count++] = p;
      p++;
    } else {
      ak++;
      p++;
    }
  }
  cout << count << endl;
  for (int i = 0; i < count; i++) cout << b[i] << ' ';
  cout << endl;
  return 0;
}
