Binary Search

using System;
using System.Linq;

class BinarySearch
{
    static void Main()
    {
        int[] numbers = Console.ReadLine().Split().Select(int.Parse).ToArray();
        int search = int.Parse(Console.ReadLine());

        int index = CustomBinarySearch(numbers, 0, numbers.Length - 1, search);
        if (index < 1)
        {
            Console.WriteLine(index);
        }
        else
        {
            index = CheckIfLeftmost(numbers, index);
            Console.WriteLine(index);
        }

    }

    static int CustomBinarySearch(int[] arr, int min, int max, int keyValue)
    {
        int middleIndex = (min + max) / 2;
        if (min >= max && arr[middleIndex] != keyValue)
        {
            return -1;
        }
        if (arr[middleIndex] == keyValue)
        {
            return middleIndex;
        }
        if (keyValue < arr[middleIndex])
        {
            return CustomBinarySearch(arr, min, middleIndex - 1, keyValue);
        }
        return CustomBinarySearch(arr, middleIndex + 1, max, keyValue);
    }

    static int CheckIfLeftmost(int[] arr, int index)
    {
        int leftMost = index;
        for (int i = index; i >= 1; i--)
        {
            if (arr[i] == arr[i - 1])
            {
                leftMost = i - 1;
            }
        }

        return leftMost;
    }
}