$a = [40, [194, [23, 234, 500], 57], 93, 39, [10, 333, 49]];
$max = 0;
foreach ($a as $b) {
    if (is_array($b)) {
        foreach ($b as $c) {
            if (is_array($c)) {
                foreach ($c as $d) {
                    $max = $d > $max ? $d : $max;
                }
            } else {
                $max = $c > $max ? $c : $max;
            }
        }
    } else {
        $max = $b > $max ? $b : $max;
    }
}
return $max;