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

dp = [{} for x in range(n)]

def solve(i, w):
    if -1 < i - 2 < n: w += a[i - 2]
    if i >= n: return w

    if dp[i].get(w):
        return dp[i][w]
    dp[i][w] = w

    return max(solve(i + 2, w), solve(i + 3, w))

print(solve(0, 0))