<?php

$list_1 = [];
$list_2 = [];

$lines = array_filter(explode("\n", file_get_contents(__DIR__.'/input.txt')), static fn($line) =>!empty($line));

foreach ($lines as $line) {
    [$a, $b] = explode("   ", $line);
    $list_1[] = $a;
    $list_2[] = $b;
}

sort($list_1); sort($list_2);
$total = 0;
for ($i=0, $l=count($list_1); $i < $l; $i++) {
    $total += abs($list_1[$i] - $list_2[$i]);
}

echo $total;