#include <bits/stdc++.h>
using namespace std;
int main(int argc, const char *argv[]) {
  int n, m;
  scanf("%d%d", &n, &m);
  vector<int> a(n);
  for (int i = 0; i < n; i++) {
    scanf("%d", &a[i]);
  }
  sort(a.begin(), a.end());
  vector<long long> answ;
  long long ci = 0, cc = 1;
  while (m >= cc) {
    if (ci < n && a[ci] == cc) {
      ci++;
    } else {
      m -= cc;
      answ.push_back(cc);
    }
    cc++;
  }
  printf("%d\n", answ.size());
  for (int i = 0; i < answ.size(); i++) {
    printf("%ld ", answ[i]);
  }
}
