#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m;
  cin >> n >> m;
  vector<long long> used(n);
  vector<long long> answ;
  for (auto &x : used) cin >> x;
  sort(used.begin(), used.end());
  long long t = 0;
  long long sum = 0;
  for (long long i = 0; i < 1e9; i++) {
    if (t < n && used[t] == i + 1)
      t++;
    else {
      sum += i + 1;
      if (sum <= m)
        answ.push_back(i + 1);
      else
        break;
    }
  }
  cout << answ.size() << endl;
  for (auto x : answ) {
    cout << x << " ";
  }
  cin >> n;
  return 0;
}
