function changeli() {
	var totalli = $("#staerke1 li").size()+1;
	$("#test").attr("value",totalli);
	console.log(totalli);
}

$("#staerke1 li,#staerke2 li").click(function () {
	$(this).css({backgroundColor: "#ddd",fontWeight: "bold"});
	changeli();
});


<input type="button" id="test" value="testbutton">