<?php

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

$count = 0;

do {
    $local_count = 0;
    $removed_papers = [];
    foreach ($grid as $i => $line) {
        foreach ($line as $j => $cell) {
            switch ($cell) {
                case '@':
                    if (count_adjacents($i, $j) < 4) {
                        $local_count++;
                        $removed_papers[] = [$i, $j];
                    }
                    break;
                case '.':
                default:
                    break;
            }
        }
    }

    foreach ($removed_papers as $removed_paper) {
        $grid[$removed_paper[0]][$removed_paper[1]] = '.';
    }

    $count += $local_count;
} while ($local_count !== 0);

echo $count;

function count_adjacents(int $i, int $j): int
{
    global $grid;
    $count = 0;
    if (array_key_exists($i - 1, $grid)) {
        if (array_key_exists($j - 1, $grid[$i - 1]) && $grid[$i - 1][$j - 1] === '@') $count++;
        if ($grid[$i - 1][$j] === '@') $count++;
        if (array_key_exists($j + 1, $grid[$i - 1]) && $grid[$i - 1][$j + 1] === '@') $count++;
    }

    if (array_key_exists($j - 1, $grid[$i]) && $grid[$i][$j - 1] === '@') $count++;
    if (array_key_exists($j + 1, $grid[$i]) && $grid[$i][$j + 1] === '@') $count++;

    if (array_key_exists($i + 1, $grid)) {
        if (array_key_exists($j - 1, $grid[$i + 1]) && $grid[$i + 1][$j - 1] === '@') $count++;
        if ($grid[$i + 1][$j] === '@') $count++;
        if (array_key_exists($j + 1, $grid[$i + 1]) && $grid[$i + 1][$j + 1] === '@') $count++;
    }
    return $count;
}