using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        int[] arr = { -1, 0, 1, 2, 4, 10 };

        Console.WriteLine(MagicIndex(arr, 0, arr.Length));

    }

    public static int MagicIndex(int[] arr, int start, int end)

    {

        if (start > end)

            return -1;

        int mid = (start+end)/2;

        if (arr[mid] == mid)

        {

            return mid;

        }

        else if (arr[mid] > mid)

        {

            return MagicIndex (arr, start, mid-1);

        }

        else

        {

            return MagicIndex (arr, mid+1, end);

        }

    }

}