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

if N == 1:
    print(V[0])
else:
    ans = [0] * (N + 1)
    ans[1] = V[0]
    for i in range(2, N + 1):
        ans[i] = max(ans[i - 1], ans[i - 2] + V[i - 1])

    print(ans[N])