#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n, m, i, k = 0, j = 1, q, l = 0, r = 2000000000000000007;
  cin >> n >> m;
  map<long long, long long> p;
  vector<long long> v;
  for (i = (1); i <= (n); i++) cin >> k, p[k] = 1;
  while (m - j >= 0) {
    if (p[j]) {
      j++;
      continue;
    } else
      m -= j, v.push_back(j), j++;
  }
  cout << v.size() << '\n';
  for (auto e : v) cout << e << ' ';
}
