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

if n >= 2:
    dp = [0] * n
    dp[0] = e[0]
    dp[1] = e[1]
    for i in range(n):
        dp[i] = max(dp[i - 1], dp[i - 2] + e[i])
    print(dp[n - 1])
else:
    print(e[0])