<?php


error_reporting(-1);
mb_internal_encoding('utf-8');
$amount = 6600;
$bills = array(
	100   => 23,
	200   => 3,
	500   => 1,
	1000  => 0,
	2000  => 4,
	5000  => 1
	);
	$bills = array_reverse($bills, true);
	//var_dump($bills);
	echo "Выдача возможна, число купюр:\n";
	foreach ($bills as $nominal => $number) {
		$quantity = floor($amount / $nominal);
		if ($number >= $quantity) {
			$amount = $amount - ($quantity * $nominal);
			$delivery = $quantity;
		}
		else {
			$amount = $amount - ($number * $nominal);
			$delivery = $number;
		}
		$x = 'x';
		echo "$delivery$x$nominal ";
	}