建堆之后堆顶是几

把 [17, 24, 15, 13, 23] 建成大顶堆。运行下面这段程序：

def sift_down(h, i, n):
    while True:
        big = i
        l = 2 * i + 1
        r = 2 * i + 2
        if l < n and h[l] > h[big]:
            big = l
        if r < n and h[r] > h[big]:
            big = r
        if big == i:
            return
        h[i], h[big] = h[big], h[i]
        i = big

h = [17, 24, 15, 13, 23]
n = len(h)
for i in range(n // 2 - 1, -1, -1):
    sift_down(h, i, n)
print(h[0])