import sys

sys.setrecursionlimit(10 ** 6)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))

def main():
    def dfs(xx=[]):
        if len(xx)==n//2:
            res=0
            for x in xx:
                res^=x
            return res
        i=used.index(False)
        used[i]=True
        res=0
        for j in range(i+1,n):
            if used[j]:continue
            used[j]=True
            ret=dfs(xx+[aa[i]+aa[j]])
            if ret>res:res=ret
            used[j]=False
        used[i]=False
        return res

    n=II()
    aa=LI()
    used=[False]*n
    print(dfs())

main()