#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
int a[100000];
vector<int> toy;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < n; ++i) cin >> a[i];
  sort(a, a + n);
  int i = 0, num = 1;
  while (m > 0) {
    if (num != a[i]) {
      m -= num;
      if (m >= 0) toy.push_back(num);
    } else
      ++i;
    ++num;
  }
  cout << toy.size() << endl;
  for (int i : toy) cout << i << " ";
  return 0;
}
