using System;

public class Program

{

    public static void Main()

    {

        int[] nums = new int[] {0,0,0,1,0,1,1,0,1};

        Console.WriteLine(Count1(nums));

    }

    public static int Count1(int[] arr)

    {

        return Count1(arr, 0);

    }

    public static int Count1(int[] arr, int index)

    {

        int counter = 0;

        if(index == arr.Length) return 0;

        if(arr[index] == 1) return (counter + 1) + Count1(arr, index + 1);

        return counter + Count1(arr, index + 1);

    }

}