n=int(input())
V=list(map(int,input().split()))

ans=0
for i in range(2**n):
    tmp,flag=0,False
    for j in range(n):
        if i>>j&1:
            if flag:
                continue
            else:
                tmp+=V[j]
                flag=True
        else:
            flag=False
    ans=max(ans,tmp)
print(ans)