from collections import defaultdict
n = int(input())
*a, = map(int,input().split())
d = {2**n-1:0}
for _ in range(n//2):
    nd = defaultdict(int)
    for k,v in d.items():
        idx = (k&-k).bit_length() - 1
        k &= k-1
        for i in range(idx+1,n):
            if k>>i&1:
                nk = k^(1<<i)
                nd[nk] = max(nd[nk], v + (a[idx]^a[i]))
    d = nd
print(d[0])