[jQuery] How do I subtract 64 pixels from the value of a div's height?

[jQuery] How do I subtract 64 pixels from the value of a div's height?


Here is my code:
$(document).ready(function () {
    var contentDivHeight = $('#contentDiv').css('height');
// pseudo-code: var calculatedHeight = ????
    $("#clickMe").click(function(){
        $("#leftNavBox-contentPages").animate({"height": calculatedHeight},
"fast");
    });
});
I need the value of calculatedHeight to be 64 pixels less than
contentDiv. So, if contentDiv is 600px, calculatedHeight needs to be
536px.
Jeremy