;Create an array of Last day of each month with builtin leapyar check
$o=0,3-(Not(@Year Mod 400) Or (@Year Mod 100) And Not(@Year Mod 4)),0,1,0,1,0,0,1,0,1,0
 
;Get Last day of the current month from $o array
$d=31-$o[@MonthNo-1]