#include <bits/stdc++.h>
using namespace std;
int main() {
  long long sum, n, m;
  cin >> n >> m;
  sum = m;
  set<long long> was;
  for (int i = 0; i < n; i++) {
    long long x;
    cin >> x;
    was.insert(x);
  }
  sum = 0;
  vector<long long> ans;
  int count = 1;
  while (true) {
    if (sum + count > m) {
      break;
    } else {
      if (was.find(count) == was.end()) {
        ans.push_back(count);
        sum += count;
      }
      count++;
    }
  }
  cout << ans.size() << endl;
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i] << ' ';
  }
}
