n = int(input())
v = [int(x) for x in input().split()]

res = 0
su = [0] * n
for i in range(n):
    if i == 0:
        su[0] = v[0]
    elif i == 1:
        su[1] = max(v[0], v[1])
    elif i == 2:
        su[2] = su[0] + v[2]
    else:
        su[i] = v[i] + max(su[i - 2], su[i - 3])
    res = max(su[i], res)

print(res)