N = int(input())
V = [int(i) for i in input().split()]
if N == 1:
    print(V[0])
else:
    dp = [0] * (N + 1)
    dp[1] = V[0]
    for i in range(2, N + 1):
        dp[i] = max(dp[i - 1], dp[i - 2] + V[i - 1])
    print(dp[N])