program main
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int32):: n,n2,s,ns,i,j,f
    integer(int32), allocatable:: a(:),dp(:)

    read*, n
    n2 = lshift(1,n)-1
    allocate(a(n))
    allocate(dp(0:n2), source=0)
    read*, a(:)
    do s=0,n2
        do i=1,n-1
            if (btest(s,i-1)) cycle
            do j=i+1,n
                if (btest(s,j-1)) cycle
                ns = ibset(ibset(s,i-1),j-1)
                f = xor(a(i),a(j))
                dp(ns) = max(dp(ns), dp(s)+f)
            end do
        end do
    end do
    print'(i0)', dp(n2)
end program main