다음 Python 프로그램의 실행 결과를 쓰시오.

class Node:
    def __init__(self, value):
        self.value = value
        self.children = []

def build(values):
    nodes = [Node(value) for value in values]
    for index in range(1, len(nodes)):
        nodes[(index - 1) // 2].children.append(nodes[index])
    return nodes[0]

def odd_level_sum(node, level=0):
    own = node.value if level % 2 == 1 else 0
    return own + sum(odd_level_sum(child, level + 1)
                     for child in node.children)

root = build([3, 5, 8, 12, 15, 18, 21])
print(odd_level_sum(root))