public class OrderService {

    public double calculateTotal(double price, int quantity) {
        assert price >= 0 : "Price must be non-negative";
        assert quantity > 0 : "Quantity must be positive";

        return price * quantity;
    }

    public double applyDiscount(double total, double discountPercent) {
        if (discountPercent < 0 || discountPercent > 50) {
            throw new IllegalArgumentException("Invalid discount");
        }

        return total - (total * discountPercent / 100);
    }

    public String categorizeOrder(double total) {
        if (total < 100) {
            return "SMALL";
        } else if (total < 500) {
            return "MEDIUM";
        } else {
            return "LARGE";
        }
    }

    public boolean isFreeShipping(double total) {
        return total >= 200;
    }
}