reverse counter

How to write reverse counter code. i want my number count 100 to 0 (reverse count)

Code:

$({countNum: $('#counter').text()}).animate({countNum: 10}, {
duration: 10000,
easing:'linear',
step: function() {
$('#counter').text(Math.floor(this.countNum));
},
complete: function() {
window.location = "http://www.google.com";
}
});

Thanks in advance