__ __ __ __ __ __ 01
02 03 04 05 06 07 08
09 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31 __ __ __ __ __

<?php
$handle = fopen("input.txt", "r");
list($month,$year) = fscanf($handle, "%d %d");

$time = mktime(0, 0, 0, $month, 1, $year);

$countDayOfMonth = date('t', $time);
$weekNum = date('w', $time) - 1;
if ($weekNum < 0) $weekNum = 6;

$countPlaces = (ceil(($countDayOfMonth + $weekNum) / 7) * 7 - ($countDayOfMonth + $weekNum)) + ($countDayOfMonth + $weekNum);

$str = "";
for($i = 1; $i <= $countPlaces; $i++)
{
    if( ($i <= $weekNum) OR $i > ($countDayOfMonth + $weekNum))
    {
        $str .= "__ ";
    }else
        $str .= str_pad(($i - $weekNum), 2, '0', STR_PAD_LEFT) . " ";

    if(($i % 7) == 0)
    {
        $str = trim($str);
        if($i < $countPlaces)
            $str .= PHP_EOL;
    }
}
echo $str;
fclose($handle);