var small_Logo_link = "obrazky/motonova_small.jpg";
var normal_Logo_link = "obrazky/motonova_normal.jpg";
function setLogo() {
   var width;
   if(window.innerWidth) {
      width = window.innerWidth;
   }
   else if(document.documentElement.clientWidth) {
      width = document.documentElement.clientWidth;
   }

   else if(document.body.clientWidth) {
      width = document.body.clientWidth;
   }
   var logo_size = document.getElementById("logo_size");
   var useSmall = (width < 1200 );
 
   logo_size.setAttribute("src", (useSmall ? small_Logo_link : normal_Logo_link));
}