def prod_signs(arr):
    if not arr: return None
    prod = 0 if 0 in arr else (-1) ** len(list(filter(lambda x: x < 0, arr)))
    return prod * sum([abs(i) for i in arr])
from typing import List
def below_zero(operations: List[int]) -> bool:
    balance = 0
    for op in operations:
        balance += op
        if balance < 0:
            return True
    return False