#include <bits/stdc++.h>
using namespace std;
int ch[10000001] = {0};
int main() {
  long long int n, m, i;
  cin >> n >> m;
  for (i = 0; i < n; i++) {
    long long int x;
    cin >> x;
    if (x < 10000000) ch[x] = 1;
  }
  long long int ind = 1, cnt = 0, j = 0, a[100000];
  while (m >= ind) {
    if (!ch[ind]) {
      m -= ind;
      cnt++;
      a[j] = ind;
      j++;
    }
    ind++;
  }
  cout << cnt << endl;
  for (i = 0; i < cnt; i++) cout << a[i] << " ";
  return 0;
}
