def maxSum(a):
    n = len(a)
    if n == 0:
        return 0
    if n == 1:
        return a[0]
    dp = [0] * n
    dp[0] = a[0]
    dp[1] = max(a[0], a[1])
    for i in range(2, n):
        dp[i] = _______________
    return dp[-1]