https://twitter.com/yacatuco/status/1438794656746254338

bad_elves_1.pl

#!/usr/bin/perl

use strict;
use warnings;

my $n = shift;

my @offsets;
my $offset = 2 - ($n & 1);
my $size = $n;

while ($size > $offset) {
    unshift @offsets, $offset;
    $size -= $offset;
    $offset = (3 - $size % 3) % 3;
    $size = int(($size + 2) / 3);
}

my $i = $size - 1;
for my $offset (@offsets) {
    $i = $i * 3 + $offset;
}

print(($i + int($n/2)) % $n + 1, "\n");