#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
using namespace std;
long long int MOD = 998244353;
double eps = 1e-12;
void solve();
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
void solve() {
  long long int n, m, a;
  vector<bool> toy(1000000000 + 1, false);
  cin >> n >> m;
  for (long long int i = 0; i < n; i++) {
    cin >> a;
    toy[a - 1] = true;
  }
  vector<long long int> v;
  int i = 0;
  while (i < 1000000000 + 1) {
    if (toy[i] == false) {
      if (m >= i + 1) {
        m = m - (i + 1);
        v.push_back(i + 1);
      } else
        break;
    }
    i++;
  }
  cout << v.size() << endl;
  for (long long int i = 0; i < v.size(); i++) {
    cout << v[i] << " ";
  }
}
