using System;

​

public class Program

{

    public static void Main()

    {

        int[] arr = {0, 0, 0, 0, 0, 1, 1, 1, 1};

        int mid;

        int left = 0;

        int right = arr.Length;

        while (right >= left)

        {

            mid = (right + left) / 2;

            if (arr[mid] == 0)

                if (arr[mid + 1] == 1)

                    Console.WriteLine(mid);

            if (arr[mid] == 1)

                right = mid - 1;

            left = mid + 1;

        }

​

        Console.WriteLine(-1);

    }

}