#include <bits/stdc++.h>
using namespace std;
char str[50];
pair<int, pair<int, char*> > p[100001];
long long c[100005];
vector<int> ans;
map<int, int> mp;
int main() {
  std::ios::sync_with_stdio(false);
  long long n, m, x;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> c[i];
  }
  sort(c, c + n);
  int j = 1;
  while (m > 0 && j < c[0]) {
    m = m - j;
    if (m >= 0) ans.push_back(j);
    j++;
  }
  c[n] = 1000000002;
  if (m > 0) {
    for (int i = 0; i < n; i++) {
      j = c[i] + 1;
      while (m > 0 && j < c[i + 1]) {
        m = m - j;
        if (m >= 0) ans.push_back(j);
        j++;
      }
      if (m <= 0) break;
    }
  }
  cout << ans.size() << "\n";
  for (int i = 0; i < ans.size(); i++) cout << ans[i] << " ";
  return 0;
}
