试图在python中实现Nilakantha算法

import math
from decimal import *

pi = Decimal(3)

two = 2
three = 3
four = 4

times = 10000

for c in range(times):
    pi += Decimal(4)/two * three * four
    pi -= Decimal(4)/two + 2 * three + 2 * four + 2 * three

    two += 2
    three += 2
    four += 4

print(pi)

它总是返回39983.4247879279112354716423 任何想法，为什么这不起作用？