using System;

public class Program

{

    public static void Main()

    {

        var amount = 600M;

        var discount = 10;

        Console.WriteLine(CalculateAmount(amount, discount).ToString("c"));

    }

    private static decimal CalculateAmount(decimal invoiceTotalCost, int discount = 0)

    {

        var discountAmount = 0M;

        if (discount >= 1)

        {

            Console.WriteLine("discount is {0}", discount);

            discountAmount = discount / 100M;

            Console.WriteLine("discount amount is {0}", discountAmount);

        }

        Console.WriteLine(discountAmount.ToString());

​

        var finalAmount = (discountAmount != 0) ? invoiceTotalCost * discountAmount : invoiceTotalCost;

        return (decimal)finalAmount;

    }

}