#include <bits/stdc++.h>
using namespace std;
long long n, m, a[100005], cur = 1;
vector<long long> v;
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  for (int i = 0; i < 1000000007; i++) {
    if (cur == a[i]) {
      cur++;
      continue;
    }
    if (m - cur < 0) break;
    if (a[i] > cur) {
      v.push_back(cur);
      m -= cur, i--, cur++;
    } else
      v.push_back(cur), m -= cur, cur++;
  }
  cout << v.size() << endl;
  for (int i = 0; i < v.size(); i++) cout << v[i] << ' ';
  cout << endl;
  return 0;
}
