def read_node(it):
    child_count, meta_count = next(it), next(it)
    if child_count == 0:
        return sum(next(it) for _ in range(meta_count))

    children = [read_node(it) for _ in range(child_count)]

    value = 0
    for _ in range(meta_count):
        index = next(it)
        if index > 0 and index <= len(children):
            value += children[index - 1]

    return value


it = (int(x) for x in input().split())
print(read_node(it))