using System;

​

public class Candies

{

    public static int CountCandies(int startingAmount, int newEvery)

    {

        var diff = (double)startingAmount / Math.Abs(-newEvery + 1);

​

        // ReSharper disable once CompareOfFloatsByEqualityOperator

        if (diff == startingAmount)

        {

            return (startingAmount * 2) - 1;

        }

​

        var truck = Math.Truncate((diff % 1) * newEvery);

        var value = Math.Truncate((diff - (diff % 1)) * newEvery);

​

        // ReSharper disable once CompareOfFloatsByEqualityOperator

        var smallDiff = truck == 0 ? -1 : truck;

​

        var maxCandies = (int)(smallDiff + value);

​

        return maxCandies;

    }

​

    public static void Main(string[] args)

    {

        Console.WriteLine(Candies.CountCandies(100, 18));

    }

}