#include <bits/stdc++.h>
using namespace std;
const int MAXN = 2e6 + 7;
bool mk[MAXN];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n, m;
  cin >> n >> m;
  for (int i = (1); i <= (n); ++i) {
    int a;
    cin >> a;
    if (a <= 2e6) mk[a] = true;
  }
  vector<int> ans;
  for (int i = (1); i <= (2e6); ++i)
    if (i <= m && !mk[i]) ans.push_back(i), m -= i;
  cout << ((int)(ans).size()) << '\n';
  for (auto x : (ans)) cout << x << ' ';
  return 0;
}
