#include <bits/stdc++.h>
using namespace std;
int n, sum, bought[100010], mtypes[200010], inc;
bool binSrc(int val) {
  int st = 1;
  int dr = n;
  bool mfound = false;
  while (st <= dr) {
    int mid = (st + dr) / 2;
    if (bought[mid] == val) {
      mfound = true;
      break;
    } else if (val > bought[mid])
      st = mid + 1;
    else
      dr = mid - 1;
  }
  return mfound;
}
int main() {
  cin >> n >> sum;
  for (int i = 1; i <= n; i++) cin >> bought[i];
  sort(bought + 1, bought + n + 1);
  int i = 1;
  while (sum - i >= 0) {
    if (!binSrc(i)) {
      sum -= i;
      mtypes[++inc] = i;
    }
    i++;
  }
  cout << inc << "\n";
  for (int i = 1; i <= inc; i++) cout << mtypes[i] << " ";
  return 0;
}
