#include <bits/stdc++.h>
using namespace std;
int gcd(int a, int b) {
  while (a && b) {
    a %= b;
    swap(a, b);
  }
  return a + b;
}
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> used(4000050);
  for (int i = 0; i < n; i++) {
    int a;
    cin >> a;
    if (a < 4000050) used[a] = 1;
  }
  vector<int> ans;
  for (int i = 1; i < 4000050; i++) {
    if (used[i] == 0 && m - i >= 0) {
      used[i] = 1;
      m -= i;
      ans.push_back(i);
    } else if (m - i < 0) {
      break;
    }
  }
  cout << ans.size() << "\n";
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i] << " ";
  }
  return 0;
}
