#include <bits/stdc++.h>
using namespace std;
long long int inf = 998244353;
int main() {
  long long int n, m, i, j, k, l, a;
  cin >> n >> m;
  map<long long int, long long int> mp;
  for (i = 0; i < n; i++) {
    cin >> a;
    mp[a]++;
  }
  long long int cost = 0;
  vector<long long int> v;
  i = 1;
  while (1) {
    if (mp[i] == 0) {
      cost = cost + i;
      if (cost < m) {
        v.push_back(i);
      } else if (cost == m) {
        v.push_back(i);
        break;
      } else if (cost > m) {
        break;
      }
    }
    i++;
  }
  cout << v.size() << endl;
  for (i = 0; i < v.size(); i++) {
    cout << v[i] << " ";
  }
}
