https://kompege.ru/variant?kim=25026733

import sys
from functools import lru_cache

sys.setrecursionlimit(3000)
@lru_cache
def f(x):
    if x >= 4040:
        return x
    if x < 4040:
        return x + 4 + f(x + 4)
print(f(3) - f(15))