#include <bits/stdc++.h>
using namespace std;
int main() {
  map<int, int> m;
  m.clear();
  int n, b;
  scanf("%d%d", &n, &b);
  for (int i = 0; i < n; i++) {
    int value;
    scanf("%d", &value);
    m[value] = 1;
  }
  int ans = 0;
  vector<int> v;
  for (int i = 1; i < 100000000 && b > 0; i++) {
    if (m[i] == 1)
      continue;
    else {
      if (b >= i) {
        ans++;
        v.push_back(i);
        b -= i;
      } else
        break;
    }
  }
  printf("%d\n", ans);
  for (int i = 0; i < v.size(); i++) printf("%d ", v[i]);
  return 0;
}
