import itertools
N = int(input())
first = input()
binary_list=[]
split_first = first.split()
cnt=round(N/2)
word_list1=list(itertools.combinations(split_first,2))
word_list2=list(itertools.combinations(word_list1,cnt))
for i in word_list2:
    chk_list=[]
    binary=0
    for j in i:
        binary+=int((bin(int(j[0])^int(j[1]))),2)

        for k in j:
            chk_list.append(k)
        
    if len(chk_list) == len(set(chk_list)):
        binary_list.append(binary)
print(max(binary_list))