n = int(input())
vs = list(map(int, input().split(' ')))

dp = [-1] * (n + 1)

dp[0] = 0
dp[1] = vs[0]

for i in range(2, n + 1):
    dp[i] = max([
        dp[i - 1],
        dp[i - 2] + vs[i - 1]
    ])

print(dp[n])