using System;

public class Program

{

    public static void Main()

    {

        int[] nums={2,1,1,2};//{1,1,1,2,0,4,10}

        int a=0,b=0;

        bool bigger = false;

        if(nums.Length==1) Console.WriteLine(nums[0]);

        for(var i=0 ; i<nums.Length ; i++)

        {

            if(i%2==0) {

                if(b>a+nums[i])

                    bigger = true;

                a = Math.Max(a+nums[i], b);//a+=nums[i];

            }

            else{

                b = Math.Max(a, b+nums[i]);//b+=nums[i];            

            }

        }

        if(!bigger && nums.Length%2!=0)

            Console.WriteLine(Math.Max(a-nums[nums.Length-1],b));

        else

            Console.WriteLine(Math.Max(a,b));

    }

}