function minAvgTwoSlice(array $a): int
{
    $idx    = 0;
    $min = ($a[0] + $a[1]) / 2;
    for ($i = 0, $count = count($a); $i < $count - 1; $i++) {
        $cur = ($a[$i] + $a[$i + 1]) / 2;
        if (isset($a[$i + 2])) {
            $three = ($a[$i] + $a[$i + 1] + $a[$i + 2]) / 3;
            $cur  = $cur < $three ? $cur : $three;
        }
        if ($cur < $min) {
            $min = $cur;
            $idx    = $i;
        }
    }

    return $idx;
}