using System;

public class Program

{

    public static void Main()

    {

        int[] array = {1,2,3,8,9};

        var result = BinarySearch(array,8);

        Console.WriteLine(result);

    }

    public static int BinarySearch(int[] array,int target)

    {

        if(array.Length == 0)

        {

            return -1;

        }

        int left = 0;

        int right = array.Length -1;

        while(left <=right)

        {

            int mid = (left+right)/2;

            if(array[mid] == target)

            {

                return mid;

            }

            else if (mid < target)

            {

                left = mid+1;               

            }

            else

            {

                right = mid-1;

            }

        }

        return -1;

    }

}