#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<double, double>;
using vi = vector<int>;
using vii = vector<pii>;
using vs = vector<string>;
const double PI = acos(-1.0);
const double EPS = 1e-14;
const int MOD = 1e9 + 7;
const int INF = 1e9;
const ll INFLL = 4e18;
const int MAX = 1e5;
int n, m;
set<int> hv, ans;
void read() {
  cin >> n >> m;
  for (int i = 0; i < (int)n; i++) {
    int t;
    cin >> t;
    hv.insert(t);
  }
}
void solve() {
  for (int i = (int)1; i <= (int)1e9; i++) {
    if (i > m) break;
    if (!(hv.find(i) != hv.end())) {
      ans.insert(i);
      m -= i;
    }
  }
  cout << (int)ans.size() << "\n";
  for (int t : ans) {
    cout << t << " ";
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int TC = 1;
  while (TC--) {
    read();
    solve();
  }
}
