n = int(input())
v = [int(s) for s in input().split()]
dp = [0] * n
maxv = 0

for i in range(n):
    dp[i] += v[i]
    maxv = max(maxv, dp[i])

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

print(maxv)