#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  bool a[200002];
  for (int i = 0; i < (int)n; i++) {
    int x;
    cin >> x;
    if (x < 200002) a[x] = 1;
  }
  vector<int> ans;
  int i = 1;
  while (m - i >= 0) {
    if (!a[i]) {
      ans.push_back(i), m -= i;
    }
    i++;
  }
  cout << ans.size() << endl;
  if (ans.size()) cout << ans[0];
  for (int j = 1; j < (int)ans.size(); j++) cout << " " << ans[j];
}
