#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, m, res = 0;
  cin >> n >> m;
  vector<long long int> a(n + 1);
  bool is[1000002];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] <= 1000001) {
      is[a[i]] = 1;
    }
  }
  int br[100001];
  for (int i = 1; i <= m; i++) {
    if (!is[i] && m) {
      br[res] = i;
      res++;
      m -= i;
      if (m < i + 1) break;
    }
  }
  cout << res << endl;
  for (int i = 0; i < res; i++) {
    cout << br[i] << " ";
  }
  return 0;
}
