n = int(input())
*a, = map(int,input().split())

def dfs(k,v):
    if k==0:
        return v
    c = 0
    idx = (k&-k).bit_length() - 1
    k ^= 1<<idx
    for i in range(idx+1,n):
        if k>>i&1:
            c = max(c,dfs(k^(1<<i),v^(a[idx]+a[i])))
    return c

print(dfs(2**n-1,0))