N = int(input())
V = [int(x) for x in input().split(" ")]

d = [0 for i in range(N + 1)]
d[1] = V[0]
choice = [[False for i in range(len(V))]]

for i in range(2, N + 1):
    d[i] = max(d[i - 1], d[i - 2] + V[i - 1])


print(d[N])