#include <bits/stdc++.h>
using namespace std;
long long n, a[100100], M;
vector<long long> res;
int main() {
  cin >> n >> M;
  for (int i = 1; i <= n; i++) cin >> a[i];
  sort(a + 1, a + n + 1);
  long long cur = 1, cnt = 0, i = 1;
  while (M > 0) {
    while (a[i] == cur) {
      i++;
      cur++;
    }
    if (cur > M) break;
    M -= cur;
    res.push_back(cur);
    cur++;
  }
  cout << res.size() << "\n";
  for (int i = 0; i < res.size(); i++) cout << res[i] << " ";
  return 0;
}
