#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  vector<bool> have(1e9 + 1, false);
  cin >> n >> m;
  int t;
  for (int i = 0; i < n; i++) {
    scanf("%d ", &t);
    have[t] = true;
  }
  int mn = 0;
  vector<int> tn;
  int k = 0;
  int j = 1;
  while (mn + j <= m) {
    if (!have[j]) {
      tn.push_back(j);
      mn += j;
    }
    j++;
  }
  k = tn.size();
  cout << k << endl;
  for (int i = 0; i < k; i++) {
    printf("%d ", tn[i]);
  }
}
