#include <bits/stdc++.h>
template <typename T>
T gcd(T a, T b) {
  if (!b) return a;
  return gcd(b, a % b);
}
template <typename T>
T lcm(T a, T b) {
  return a * b / gcd(a, b);
}
template <typename T>
void chmin(T& a, T b) {
  a = (a > b) ? b : a;
}
template <typename T>
void chmax(T& a, T b) {
  a = (a < b) ? b : a;
}
int in() {
  int x;
  scanf("%d", &x);
  return x;
}
using namespace std;
int N, M;
unordered_map<int, bool> seen;
int main(void) {
  cin >> N >> M;
  for (int i = 0; i < N; i++) {
    int tp;
    cin >> tp;
    seen[tp] = true;
  }
  vector<int> ans;
  for (int i = 1; i <= 200000; i++) {
    if (!seen[i]) {
      if (M - i < 0) {
        break;
      }
      ans.push_back(i);
      M -= i;
    }
  }
  cout << ans.size() << "\n";
  for (int i = 0; i < (int)ans.size(); i++) {
    cout << ans[i] << " ";
  }
  cout << "\n";
  return 0;
}
