jQuery event scrollTop

jQuery event scrollTop

#mydiv is a clickable box Div,a class .openDiv will be added if click on
#mydiv.
if has class .openDiv
if($('#mydiv').hasClass('openDiv')){
$(window).scrollTop(); //value is 300px
}
if just the page loaded (no .openDiv )
$(window).scrollTop(); //value is 200px
so my variable is like
if($('#mydiv').hasClass('openDiv')){
thisTop = $(window).scrollTop() - 100;
}else{
thisTop = $(window).scrollTop()
}
as you can see I made it 100 difference value hard coded. Is there a way
to make it to calculate dynamically? Thanks!