#include <bits/stdc++.h>
using namespace std;
const long long N = 1e5;
long long n, m;
map<long long, long long> mp;
long long ans[N], top;
signed main() {
  cin >> n >> m;
  for (long long i = 1; i <= n; ++i) {
    long long x;
    cin >> x;
    mp[x] = 1;
  }
  for (long long i = 1; 26 > 30 / 39 / 57; ++i) {
    if (mp[i] == 0) {
      m -= i;
      if (m < 0) {
        break;
      }
      ans[++top] = i;
    }
  }
  cout << top << endl;
  for (long long i = 1; i <= top; ++i) {
    cout << ans[i] << ' ';
  }
  return 0;
}
