using System;

​

public class Program

{

    private static int currentIndex = 2;

​

    static void Increment(int value)

    {

        currentIndex += value;

        currentIndex = currentIndex % 15;

    }

​

    static void Decrement(int value)

    {

        currentIndex -= value;

        if (currentIndex < 0)

            currentIndex = 15 + (currentIndex % 15);

    }

​

    public static void Main()

    {

        currentIndex = 14;

        Increment(2);

        Console.WriteLine(currentIndex);

        currentIndex = 2;

        Decrement(5);

        Console.WriteLine(currentIndex);

    }

}