import sys
sys.setrecursionlimit(10**9)

N = int(input())
A = list(map(int, input().split()))

def dfs(sets, p):
    ans = []
    if not sets:
        return p
    m = min(sets)
    sets ^= {m}
    for i in sets:
        ans.append(dfs(sets^{i}, p ^ (A[m]+A[i])))
    return max(ans)

sets = set(range(N))
print(dfs(sets, 0))