using System;

public class Program

{

    public static void Main()

    {

        int[] houses = {1,2,3,1,9,10,9};

        Console.WriteLine(RobMaxAmount(houses).ToString());

    }

    public static int RobMaxAmount(int[] houses) {

        return Math.Max(RobMaxAmountSp(houses, 0, 0), RobMaxAmountSp(houses, 1, 0));

    }

    public static int RobMaxAmountSp(int[] houses, int position, int sum) {

        if(position >= houses.Length)

            return sum;

        if(position < houses.Length)

            sum += houses[position];

        return Math.Max(RobMaxAmountSp(houses, position+2, sum), RobMaxAmountSp(houses, position+3, sum));

    }

}