function changeImages() {
	   
   tmp=document.getElementById('img3').src;
   
   document.getElementById('img3').src = document.getElementById('img2').src;
   document.getElementById('img2').src = document.getElementById('img1').src;
   document.getElementById('img1').src = tmp;
}
function getDiscount(num) {
	if(num>15 && num<=21) return 3;
	else if(num>21) return 5;
	else return 0;
}

function refreshDiscount() {
	discount = getDiscount(document.getElementById('counter').value);
	tprice = document.getElementById('p').value * document.getElementById('counter').value;
	total = Math.round(tprice * discount/1000) *10;
	document.getElementById('discount').value = total + ' Руб. (' + discount + '%)';
	document.getElementById('tprice').value = tprice - total + ' Руб.';
}

function min(){
	if (document.getElementById('counter').value > 1) {
		document.getElementById('counter').value = parseInt(document.getElementById('counter').value) - 1;
	}
	refreshDiscount();
}

function add(){
	document.getElementById('counter').value = parseInt(document.getElementById('counter').value) + 1;
	refreshDiscount();
}