#include <bits/stdc++.h>
using namespace std;
int n, m, x;
vector<int> v;
set<int> bol;
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n >> m;
  for (int i = 0; i < n; i++) cin >> x, bol.insert(x);
  int now = 1;
  while (m >= now) {
    if (bol.find(now) != bol.end()) {
      now++;
      continue;
    }
    v.push_back(now);
    m -= now;
    now++;
  }
  cout << v.size() << '\n';
  for (int i = 0; i < v.size(); i++) {
    cout << v[i];
    i == v.size() - 1 ? cout << '\n' : cout << ' ';
  }
  return 0;
}
