How to change only one javascript function in wordpress child theme?

I would like to change just one JavaScript function in the child theme but without having to insert all the JavaScript code of the parent theme.

How do I change only this function (I need change only count = Math.ceil(width / size) line):

function slickAutoResponsive(slider, max, size) {    if (!max){     max = 5;   }   if (!size){     size = 380;   }    var width = slider.width(),     count = Math.ceil(width / size);    if (count < 1) count = 1;   if (count > max) count = max;    return count; }