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

if n>=3:
    lst2 = [lst[0],max(lst[0],lst[1])]
    for i in range(2,n):
        mx = max(lst2[i-2]+lst[i],lst2[i-1])
        lst2.append(mx)
    print(max(lst2[-2:]))
else:
    print(max(lst))