#include <bits/stdc++.h>
using namespace std;
int n, m;
set<int> cnt;
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; ++i) {
    int x;
    scanf("%d", &x);
    cnt.insert(x);
  }
  int ans = 0, cur = 1, mm = m;
  while (m > 0) {
    if (!cnt.count(cur)) {
      if (cur > m) {
        break;
      }
      m -= cur;
      ++ans;
    }
    ++cur;
  }
  printf("%d\n", ans);
  cur = 1;
  while (mm > 0) {
    if (!cnt.count(cur)) {
      if (cur > mm) {
        break;
      }
      mm -= cur;
      printf("%d ", cur);
    }
    ++cur;
  }
  return 0;
}
