[jQuery] Convert MooTools to jQuery

[GonzoDesign]

I know this is sloppy code, I'm more of a HTML and CSS person than
JavaScript person. The thing is this code does exactly what I need it
to do. This is done with mootools and it conflicts with some other
jQuery things going on, on the page. I would REALLY appreciate any
help anyone could give me.

This isn't the finished code implemented but if there core details of
this code could be re-written as jQuery I can probably tailor it for
the purpose I'm using it for.

window.addEvent('domready', function() {
        $('myInput').addEvent('keyup', function() {
                max_chars = 20;
                current_value   = $('myInput').value;
                current_length  = current_value.length;
                remaining_chars = max_chars-current_length;
                $('counter_number').innerHTML = remaining_chars;

                if(remaining_chars<=14){
                        $('europe').setStyle('opacity', '3.5');
                }
                else if(remaining_chars<=15){
                        $('europe').setStyle('opacity', '3');
                }
                else if(remaining_chars<=16){
                        $('europe').setStyle('opacity', '0.25');
                }
                else if(remaining_chars<=17){
                        $('europe').setStyle('opacity', '0.2');
                }
                else if(remaining_chars<=18){
                        $('europe').setStyle('opacity', '0.15');
                }
                else if(remaining_chars<=19){
                        $('europe').setStyle('opacity', '0.1');
                } else {
                        $('europe').setStyle('opacity', '0.05');
                }
        });
});