N = int(input())
A = [-1] + list(map(int, input().split()))

M = 18
inf = 1 << 60
dp = [[-inf] * (2 * M + 5) for i in range(2 * N + 5)]

for i in range(N, 0, -1):
    for j in range(-M, M):
        dp[i][j] = A[i] * j
    l = 2 * i
    r = 2 * i + 1

    for j in range(-M, M):
        res = 0
        res = max(res, dp[l][j + 1])
        res = max(res, dp[r][j + 1])
        res = max(res, dp[l][j - 1] + dp[r][j + 1])
        res = max(res, dp[l][j + 1] + dp[r][j - 1])
        dp[i][j] += res

print(dp[1][0])