#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, j, k, m, n, a, b;
  cin >> n >> m;
  int temp, arr[200005];
  for (i = 1; i <= 200005; i++) {
    arr[i] = i;
  }
  for (i = 1; i <= n; i++) {
    cin >> temp;
    if (temp <= 200000) arr[temp] = 0;
  }
  i = 1, j = 0;
  int c = 0, ans[100005];
  while (m >= i) {
    if (arr[i] != 0) {
      c++;
      j++;
      ans[j] = i;
      m = m - arr[i];
    }
    i++;
  }
  cout << j << endl;
  for (i = 1; i <= j; i++) {
    cout << ans[i] << " ";
  }
  return 0;
}
