NumberOfImagesToRotate = 26;

function change_bg() {
  if ((window.location.pathname != '/accueil')  &&
      (window.location.pathname != '/')) {
    var ran_number = Math.floor(Math.random() * (NumberOfImagesToRotate + 1));
    document.getElementById("content").style.background = 
      '#ececec url(/bg/' + ran_number + '.jpg) left top no-repeat';
    document.getElementById("main").style.paddingTop = "225px";
  }
}

window.onload = change_bg;